magnetic properties of aggregate polycrystalline diamond implications for carbonado history carbonados are aggregate polycrystalline diamonds and are found in placer deposits of the central african republic car and the bahia province of brazil their origin is uncertain but several mutually exclusive hypotheses have been proposed ranging from extraterrestrial to crustal and mantle provenance in an endeavor to further our understanding of these diamonds we performed a series of magnetic characterization studies on 20 samples from the car our results reveal that the carbonados contain material with contrasting magnetic hysteresis behavior and magnetization acid leaching permitted us to monitor the distribution of magnetic carriers within the samples an absence of sample size dependence on magnetization loss indicates that the magnetic carriers are distributed at the vitreous surface including open pores and that the carbonado interior is essentially devoid of the magnetic carriers the diamond s isolated nonmagnetic interior of carbonados suggests that the initial formation environment was deficient in magnetic particles the formation of the magnetic carriers is thus closely linked with the origin of the smooth surface perhaps during the hypervelocity ejection of carbonados into the earth s atmosphere partial ablation in the earth s primordial oxygenpoor atmosphere resulted in a fusion of the originally porous material and a decrease in the original pore density at the surface secondary mineralization of the impact generated melt and or the products of later diagenetic processes containing the majority of the magnetic carriers filled the remainder of the open pores fl 2000 elsevier science b v all rights reserved

texture analysis of sar sea ice imagery using gray level co occurrence matrices this paper presents a preliminary study for mapping sea ice patterns texture with 100 m ers 1 synthetic aperture radar sar imagery the authors used gray level co occurrence matrices glcm to quantitatively evaluate textural parameters and representations and to determine which parameter values and representations are best for mapping sea ice texture they conducted experiments on the quantization levels of the image and the displacement and orientation values of the glcm by examining the effects textural descriptors such as entropy have in the representation of different sea ice textures they showed that a complete gray level representation of the image is not necessary for texture mapping an eight level quantization representation is undesirable for textural representation and the displacement factor in texture measurements is more important than orientation in addition they developed three glcm implementations and evaluated them by a supervised bayesian classifier on sea ice textural contexts this experiment concludes that the best glcm implementation in representing sea ice texture is one that utilizes a range of displacement values such that both microtextures and macrotextures of sea ice can be adequately captured these findings define the quantization displacement and orientation values that are the best for sar sea ice texture analysis using glcm

constraining diamond metasomatic growth using c and n stable isotopes examples from namibia the present paper provides c and n stable isotope characteristics n contents and n aggregation states for alluvial diamonds of known paragenesis from placers along the namibian coast the sample set includes diamonds with typical peridotitic and eclogitic inclusions and the recently reported undetermined suite of leost et al contrib mineral petrol 145 2003 15 which resulted from infiltration of high temperature carbonate rich melts 13c values range from 20 3 to 0 5 n 48 for peridotitic diamonds and from 38 5 to 1 6 n 45 for eclogitic diamonds diamonds belonging to the undetermined suite span a narrower range in 13c from 8 5 to 2 7 n 13 when compared with previous studies diamonds from namibia are characterised by unusually low proportions of n free i e type ii peridotitic and eclogitic diamonds 3 and 2 respectively and an unprecedented high proportion of n rich diamonds 15 and 73 respectively have n contents 600 ppm 15n values for diamonds of the peridotitic eclogitic and undetermined suites range from 10 to 13 without correlations with either n content or 13c the similarity in n isotopic composition and the n rich character of diamonds belonging to the eclogitic peridotitic and undetermined suites is striking and suggests a close genetic relationship we propose that a large part of the diamonds mined in namibia formed during metasomatic events of similar style that introduced carbon and nitrogen into a range of different host lithologies

barents sea seasonal ice zone features and processes from ers 1 synthetic aperture radar seasonal ice zone experiment 1992 sea ice features and processes in the barents sea were studied during the seasonal ice zone experiment 1992 sizex92 a dedicated ers 1 satellite synthetic aperture radar sar field campaign carried out in march 1992 sizex92 was based around the research vessels polarsyssel and hakon mosby in situ oceanographic meteorological and ice measurements were made coordinated with low altitude aerial observations and ers 1 sar data acquired in near real time fifty eight low and full resolution sar scenes were obtained during sizex92 which provided a validation data set for ers 1 sar backscatter under winter conditions in the barents sea analysis of sizex92 data has provided geophysical insights including a better understanding of barents sea ice edge freezing processes and ice edge development in response to atmospheric forcings in particular areas of new ice formation were found to be related to bathymetric features through their influence on the circulation of arctic and atlantic water masses ers 1 sar image sequences revealed rapid mesoscale variations in new ice areas and the ice edge in response to wind conditions in addition to geophysical insight sizex92 demonstrated some of the technical capabilities and limitations of ers 1 sar to identify new ice areas the ice edge ice floes and ice types mapping new ice areas using satellite sar data may be considered the most promising new application the limitations of ers 1 sar derived ice classification and ice motion estimates in the marginal ice zone are identified

remobilization in the cratonic lithosphere recorded in polycrystalline diamond polycrystalline diamonds framesites from the venetia kimberlite in south africa contain silicate minerals whose isotopic and trace element characteristics document remobilization of older carbon and silicate components to form the framesites shortly before kimberlite eruption chemical variations within the garnets correlate with carbon isotopes in the diamonds indicating contemporaneous formation trace element radiogenic and stable isotope variations can be explained by the interaction of eclogites with a carbonatitic melt derived by remobilization of material that had been stored for a considerable time in the lithosphere these results indicate more recent formation of diamonds from older materials within the cratonic lithosphere

baltic sea ice sar segmentation and classification using modified pulse coupled neural networks a method for segmentation and classification of baltic sea ice synthetic aperture radar sar images based on pulse coupled neural networks pcnns is presented also automated training which is based on decomposing the total pixel value distribution into a mixture of class distributions is presented and discussed the algorithms have been trained and tested using logarithmic scale radarsat 1 scansar wide mode images over the baltic sea ice before the decomposition into mixture of class distributions an incidence angle correction specifically designed for these baltic sea ice sar images is applied because the data distributions in the uniform areas of these images are very close to gaussian distributions the data are decomposed into a mixture of gaussian distributions using the expectation maximazation algorithm only uniform image areas are used in the decomposition phase the mixture of distributions is compared to the distributions of the baltic sea ice classes based on earlier scatterometer measurements and visual video interpretations of the sea ice classes the parameter values for the pcnn segmentation are defined based on this mixture of distributions the pcnn segmentation results are also compared to the operational sea ice information of digitized ice charts and to visual interpretation of the sea ice class

radiation induced diamond crystallization origin of carbonados and its implications on meteorite nano diamonds abstract ten carbonados from central africa were studied for u th pb systematics to extract u th and pb from the samples we developed a cold combustion technique wherein diamond was burnt in liquid oxygen the technique gave low blanks 25 50 pg for pb 3 pg for u and 5 pg for th after very thorough acid treatments of the carbonados with hot hno3 hf and hcl over one week most of u th and pb were removed from the samples lead in the acid leached diamonds was highly radiogenic 206pb 204pb up to 470 however the amounts of u and th in the acid leached diamonds are too low to account for the radiogenic pb even if we assume 4 5 ga for the age of the diamonds therefore we conclude that the radiogenic pb was implanted into the diamonds from surroundings by means of recoil energy of radioactive decays of u and th from the radiogenic lead isotopic composition we estimate a minimum age of 2 6 ga and a maximum age of 3 8 ga for the formation of the carbonados the above findings of the implantation of recoiled radiogenic pb into carbonados is consistent with the process of radiation induced crystallization which was proposed for carbonado by kaminsky 1987 we show from some theoretical considerations that when highly energetic particles such as those emitted from radioactive decay of u and th interact with carbonaceous materials they give rise to cascades of atomic disturbance over regions of about a few nanometer and the disturbed atoms are likely to recrystallize to form micro diamonds because of increasing surface energy due to small size the radiation induced diamond formation mechanism may be relevant to the origin of nano diamonds in primitive meteorites

mapping of different sea ice regimes using images from sentinel 1 and alos synthetic aperture radar airborne c and l band synthetic aperture radar sar images were acquired for three test sites over different sea ice regimes around svalbard in march 2007 complemented by optical imagery environmental data and ice observations one objective was to use the high resolution low noise radar data for investigations on the technical performance of european space agency s sentinel 1 mission for sea ice mapping the other to assess the potential gain of additional use of l band sar data currently available from advanced land observing satellite alos the airborne sar images were employed to simulate data products resembling the interferometric wide swath mode iwsm of sentinel 1 and alos palsar fine resolution mode frm in order to quantify the information loss due to the higher noise level and coarser spatial resolution at the iwsm noise level zones of deformation level ice and new ice can be well separated at like polarization at cross polarization the noise level is too high for a robust automated classification including thin ice but deformed and level ice can be discriminated palsar frm is on average better suited to distinguish deformed and level ice over all ice regimes it was worse for separating new from thicker level ice at two test sites for the third test site with very few patches of new ice the palsar frm showed larger intensity contrasts between new and level ice than sentinel 1 iwsm the spatial resolution provided by the iwsm and frm is sufficient to identify most ice features and types without ambiguities typical characteristics of the imaged ice regimes are described

classification of sea ice types in envisat synthetic aperture radar images in this paper sea ice in the central arctic has been classified in synthetic aperture radar sar images from envisat using a neural network nn based algorithm and a bayesian algorithm since different sea ice types can have similar backscattering coefficients at c band hh polarization it is necessary to use textural features in addition to the backscattering coefficients the analysis revealed that the most informative texture features for the classification of multiyear ice myi deformed first year ice fyi dfyi and level fyi lfyi and open water nilas are correlation inertia cluster prominence energy homogeneity and entropy as well as third and fourth central statistical moments of image brightness the optimal topology of the nn trained for envisat wide swath sar sea ice classification consists of nine neurons in input layer six neurons in hidden layer and three neurons in output layer the classification results for a series of 20 sar images acquired in the central part of the arctic ocean during winter months were compared to expert analysis of the images and ice charts the results of the nn classification show that the average correspondences with the expert analysis amount to 85 83 and 80 for lfyi dfyi and myi respectively the bayesian pixel based method can provide a higher resolution in the classified image and therefore better capability to identify leads compared to the nn method both methods may be effectively used in the central arctic where myi is predominant

two way exchange between the easter mantle plume and the easter microplate spreading axis the conventional model whereby plume volcanism forms linear age progressive volcanic chains with the youngest activity occurring nearest a spreading axis at a hotspot has been challenged for the easter seamount chain1 4 whereas early work suggested the existence of a linear melting anomaly a hotline 1 2 more recent studies3 4 have proposed a hotspot near salas y gomez island connected with the easter microplate spreading system by an 800 km long volcanically active plume channel here we use geochemical geological and geochronological data to argue that the hotspot lies close to easter island moreover new isotopic data for lavas from the seamount chain provide evidence for bidirectional flow between the spreading axis and the plume thus supporting geophysical and fluid dynamical models of mantle flow in a plume spreading axis system5 7 material balance and flux considerations show the easter plume to be weak and cool compared with those beneath larger features such as iceland hawaii and the galapagos islands

constraints on age and construction process of the foundation chain submarine volcanoes from magnetic modeling abstract the interaction between the foundation hotspot and the pacific antarctic ridge south pacific is one of the two known cases where a ridge is approaching a hotspot this ridge hotspot relative movement results in a change in the morphology of the volcanoes along the chain as the age of the lithosphere at the time of edifice formation progressively diminishes four hundred kilometers west of the pacific antarctic ridge axis volcanism is distributed along two sub parallel lines of volcanoes separated by distances diminishing from 100 km at the west to 50 km near the axis of the ridge the magnetic anomalies mapped on this part of the chain show a pattern clearly dominated by the magnetic signature of the seamounts the anomalies were forward modeled using a remanent magnetization of normal or reversed polarity within the volcano topography the resulting pattern of normal and reversed magnetization is consistent with the intervals of the geomagnetic polarity time scale for the last 5 ma the age of the oldest studied volcano these magnetic anomalies therefore represent an independent means of dating the volcanic edifices the ages deduced from the modeling are consistent with the hypothesis of volcanoes built by a hotspot on the fast moving pacific plate and are in good agreement with the published radiometric dates although these dates tend to correspond to the late constructional stages of the edifices the differences between magnetic and radiometric ages suggest that the average time span to build a volcano of the foundation chain is about 1 million years in agreement with other intraplate edifices the difference between the magnetic ages of the seamounts and of the underlying crust both deduced from the magnetic anomaly analysis show that the ridge has approached the hotspot at a rate of 40 km ma

evidence for a mantle component shown by rare gases c and n isotopes in polycrystalline diamonds from orapa botswana in an attempt to constrain the origin of polycrystalline diamond combined analyses of rare gases and carbon and nitrogen isotopes were performed on six such diamonds from orapa botswana helium shows radiogenic isotopic ratios of r ra 0 14 1 29 while the neon ratios 21 ne 22 ne of up to 0 0534 reflect a component from mantle nucleogenic and atmospheric sources 40 ar 36 ar ratios of between 477 and 6056 are consistent with this interpretation the 129 xe 130 xe isotopic ratios range between 6 54 and 6 91 and the lower values indicate an atmospheric component the he ne ar and xe isotopic compositions and the xe isotopic pattern are clear evidence for a mantle component rather than a crustal one in the source of the polycrystalline diamonds from orapa they 13 c and y 15 n isotopic values of 1 04 to9 79xand 4 5 to 15 5x respectively lie within the range of values obtained from the monocrystalline diamonds at that mine additionally this work reveals that polycrystalline diamonds may not be the most appropriate samples to study if the aim is to consider the compositional evolution of rare gases through time our data shows that after crystallization the polycrystalline diamonds undergo both gas loss that is more significant for the lighter rare gases such as he and ne and secondary processes such as radiogenic nucleogenic and fissiogenic as well as atmospheric contamination finally if polycrystalline diamonds sampled an old mantle 1 3 2 ga the determined xe isotopic signatures which are similar to present morb mantle no fissiogenic xe from fission of 238 u being detectable imply either that xe isotopic ratios have not evolved within the convective mantle since diamond crystallization or that these diamonds are actually much younger d 2005 elsevier b v all rights reserved

comparison of enigmatic diamonds from the tolbachik arc volcano kamchatka and tibetan ophiolites assessing the role of contamination by synthetic materials abstract the enigmatic appearance of cuboctahedral diamonds in ophiolitic and arc volcanic rocks with morphology and infrared characteristics similar to synthetic diamonds that were grown from metal solvent requires a critical reappraisal we have studied 15 diamond crystals and fragments from tolbachik volcano lava flows using fourier transform infrared spectrometry ftir transmission electron microscopy tem synchrotron x ray fluorescence srxrf and laser ablation inductively coupled plasma mass spectrometry la icp ms ftir spectra of tolbachik diamonds correspond to typical type ib patterns of synthetic diamonds in tem films prepared using focused ion beam technique we find mn ni and mn si inclusions in tolbachik diamonds srxrf spectra indicate the presence of fe ni and fe ni mn inclusions with cr ti cu and zn impurities la icp ms data show variable but significantly elevated concentrations of mn fe ni and cu reaching up to 70 ppm these transition metal concentration levels are comparable with those determined by la icp ms for similar diamonds from tibetan ophiolites mn ni fe solvent was widely used to produce industrial synthetic diamonds in the former ussr and russia with very similar proportions of these metals hence it appears highly probable that the cuboctahedral diamonds recovered from kamchatka arc volcanic rocks represent contamination and are likely derived from drilling tools or other hard instruments kinetic data on diamond dissolution in basaltic magma or in fluid phase demonstrate that diamond does not form under the pressures and temperature conditions prevalent within the magmatic system beneath the modern day klyuchevskoy group of arc volcanoes we also considered reference data for inclusions in ophiolitic diamonds and compared them with the composition of solvent used in industrial diamond synthesis in china the similar inclusion chemistry close to ni70mn25co5 for ophiolitic and synthetic chinese diamonds scrutinized here suggests that most diamonds recovered from tibetan and other ophiolites are not natural but instead have a synthetic origin in order to mitigate further dubious reports of diamonds from unconventional tectonic settings and source rocks we propose a set of discrimination criteria to better distinguish natural cuboctahedral diamonds from those produced synthetically in industrial environments and found as contaminants in mantle and crust derived rocks

diamonds in volcaniclastic komatiite from french guiana the world s main sources of non alluvial diamonds are found in ultrapotassic kimberlite1 or lamproite2 diatremes pipes filled with explosive volcanic debris most of which have phanerozoic ages and are located in stable precambrian cratons diamond exploration has therefore tended to focus on such deposits microdiamonds are known to occur in metamorphic rocks such as gneiss3 and eclogite4 that have equilibrated deep in the mantle and were then tectonically transported to the surface but such deposits are thought to have little commercial potential here we report a new type of diamond occurrence from the dachine region in french guiana for which the host rock is volcaniclastic komatiite an unusual type of volcanic rock whose composition and origin are quite unlike those of kimberlite and lamproite these komatiites form part of a proterozoic island arc sequence a tectonic setting distinct from that of all other currently exploited diamond deposits the discovery of diamonds in volcaniclastic komatiite has implications not only for diamond exploration but also provides strong evidence that these komatiite magmas originated at depths of 250 km or greater within the earth

eocene propagating rifts in the southwest pacific and their conjugate features on the nazca plate we have mapped a 1200 km long nw se trending lineament in seasat and geosat radar altimeter data crossing a remote portion of the southwest pacific basin this lineament runs obliquely both to the fracture zones fzs and magnetic lineations between the austral and agassiz fzs by examining shipboard magnetics gravity and bathymetric profiles in this region and in the conjugate regions of the nazca plate we identify this feature as the site of a series of small ridge jumps highly asymmetrical spreading and small propagating rifts during the mid to late eocene chron c21 to chron c13 between the austral and agassiz fzs there is roughly 250 to 350 km of missing pacific plate crust which must have been transferred to the nazca plate by the propagating rifts and small ridge jumps on the nazca plate the conjugate area to the gravity lineament is now being subducted beneath the chile trench north of the challenger fz this area corresponds to a region of undecipherable magnetic anomalies south of the challenger fz there is evidence for a small 50 km ridge jump offshore of the chile trench this small ridge jump by itself is not sufficient to account for the missing crust on the pacific plate and we conclude that there must have been repeated small ridge jumps at the same site one consequence of these ridge jumps is that crust on the nazca plate entering the trench is not as old as would be predicted by simply mirror imaging the anomaly pattern on the pacific plate

modelling the growth of natural diamonds abstract in the following article we have reviewed the mineralogical chemical physical and isotopic evidence concerning the growth of coated diamonds and have combined it to produce a comprehensive model for their formation we suggest that the coatings formed during a period of metasomatic activity which preceded the eruption of their host kimberlites ultrapotassic co21bh2o rich fluids resulted from the crystallisation of diamond free kimberlitic magmas intruded into the deep lithosphere the kimberlite magmas were derived from an asthenospheric source which was globally quite uniform in terms of the isotopic composition of carbon and nitrogen 13c and 15n both being close to 5 the fluids produced during crystallisation invaded overlying diamondiferous lithosphere in which different regions could contain diamond populations with different mineralogical isotopic and physical characteristics depending on the history of their source region either intrinsic to their formation or due to reaction with reduced lithosphere the fluids were super saturated with carbon although not to such an extent as to allow for the nucleation of new diamonds when these super saturated fluids encountered older diamonds new and fibrous diamond growth commenced immediately this period of metasomatic activity was followed rapidly by one or more successful kimberlite eruptions which transported the now coated diamonds to the surface in the crust carbonates within hypabyssal facies kimberlites will have 13c values which reflect the deep seated source 5 whereas those within diatreme facies may be more variable due to outgassing of co2 during eruption finally we consider isotope fractionation related to growth we suggest that approaches based on equilibrium are not appropriate to diamonds but rather that it is better to consider the nature and kinetics of the surface reactions leading to growth where diamond growth is very rapid as may be the case for fibrous diamond we propose that there will be no difference in isotopic composition between the fluid and diamond and not the 3 4 13c depletion in the latter predicted by theoretical treatments octahedral diamonds are more problematic since far less is known about their growth conditions however we show in principle how the content and perhaps isotopic composition of nitrogen within a diamond may be controlled by its growth rate we are uncertain whether 13 c would be affected

evidence for recurrent early triassic massive volcanism from quantitative interpretation of carbon isotope fluctuations abstract carbon cycle disturbance associated with mass extinction at the end of the permian period continued through the early triassic an interval of approximately 5 million years coincidence of carbon cycle stabilization with accelerated middle triassic biotic recovery suggests a link between carbon cycling and biodiversity but the cause of early triassic carbon isotope excursions remains poorly understood previous modeling studies have focused exclusively on the initial negative excursion in 13c across the permian triassic boundary and have not addressed the cycles of positive and negative excursions observed through the early triassic this study uses a simple carbon cycle box model to investigate potential causes underlying the series of early triassic carbon isotope excursions and to assess possible relationships between isotope excursions and coeval patterns of carbonate deposition according to the model introduction of carbon with the isotope composition of volcanic co2 produces small negative carbon isotope excursions followed by larger and more protracted positive excursions positive excursions result because increased pco2 causes warming enhancing marine anoxia and associated regeneration of phosphate and thus allowing greater productivity in addition carbonate weathering is more sensitive than organic carbon weathering to changes in atmospheric pco2 and climate causing an increase in the overall 13c composition of weathered carbon therefore the full early triassic record of negative and positive carbon isotope excursions can only be accounted for within the model by several pulses of carbon release characterized by varying mixtures of organic and mantle isotope compositions thermal metamorphism of coal and carbonate rocks in the crust of the siberian craton during eruption of the siberian traps flood basalts provides the most plausible mechanism for such a carbon release scenario if multiple episodes of co2 release account for early triassic carbon cycle instability regardless of their precise trigger then cessation of co2 release is likely to explain acceleration of biotic recovery early in the middle triassic

the support mechanism of the young foundation seamounts inferred from bathymetry and gravity summary the youngest volcanoes of the foundation volcanic chain were built on a plate less than 5 myr near the pacific antarctic ridge par axis the progressive approach of the spreading ridge to the hotspot during the last 10 myr resulted in the building of the edifices upon a progressively younger plate estimates of the effective elastic thickness te using two independent methods show that the elastic thickness of the plate diminishes towards the spreading ridge from 5 3 km to 2 0 km the spatial variation of te correlates with a significant change in both the morphology and the volume of the volcanoes suggesting an important control of the elastic thickness on the volcanic processes the reduction in te also explains conveniently the reduction in the distance between the north and the south systems the double volcanic line that characterizes the young part of the foundation chain in the direction of young loading ages the south system formed at the top of a flexural bulge created by the emplacement of the north system the main volcanic line the low te estimate for the south system and the shape of the bouguer anomalies confirm this model the effective elastic thicknesses obtained in this study are well matched by isotherms between 200 c and 300 c and support the hypothesis of a weak plate three mechanisms possibly acted to lower the plate rigidity re heating of a normal plate by the hotspot north system local fracturing south system and the creation of a thin lithosphere at the par axis by the coupling of a hotspot and the ridge related melting zones near ridge volcanoes

plume ridge interaction revisited evidence for melt mixing from he ne and ar isotope and abundance systematics abstract submarine volcanic glass he ne and ar data from the pacific antarctic rise at its intersection with the foundation seamount chain have been obtained to further elucidate one of the main outstanding problems in plume ridge interaction studies the physical state in which mantle flow and mixing occur in those settings mixing of plume mantle and mid ocean ridge basalt source material may either be in the form of two solids of solid melt or of two melt phases only the positive correlation of 4 he 40 ar with 206 pb 204 pb as well as the negative correlation of 4 he 40 ar with 40 ar and 4 he concentrations combined with a lack of correlation between 4 he 40 ar and ridge depth or mgo concentration indicate that the enriched mantle plume material has been extensively degassed prior to mixing with the mid ocean ridge source material degassing of the plume source and mid ocean ridge source material prior to mixing is also suggested by the he versus pb isotope systematics however the occurrence of degassing processes requires the existence of melts implying that mixing between the plume and the mid ocean ridge material occurs in the physical form of melts

primary clinopyroxene spherulites in basaltic lavas from the pacific antarctic ridge fresh glassy basaltic andesite samples recovered from the northern part of the pacific antarctic ridge contain abundant spherulites consisting of arrays of closely packed clinopyroxene fibers the spherulites frequently enclose elongated vesicles that are tear drop shaped or tailed the long axes of the elongated vesicles were found to be always parallel to the orientation of the surrounding crystal fibers in several cases elongated vesicles having different orientations are hosted by a single spherulite the existence of elongated vesicles provides unequivocal evidence that a significant proportion of the clinopyroxene fibers must have crystallized directly from a supercooled liquid at temperatures above the glass transition moreover the absence of fractures within the spherulites and the surrounding glass as well as the observed nucleation of clinopyroxene fibers at vesicle walls are interpreted to be consistent with a primary origin of the clinopyroxene spherulites based on these textural observations it has to be concluded that spherulites do not represent a diagnostic texture for the devitrification of volcanic glass that occurs below the glass transition temperature

carbon nitrogen argon and helium study of impact diamonds from ebeliakh alluvial deposits and popigai crater nineteen diamond aggregate specimens 1 2 mm in size from impactites of popigai crater and five diamond samples 5 7 mm in size from ebeliakh river placers were studied our investigations indicate that samples from ebeliakh were formed in an impact event with the exception of one specimen y7 the carbon isotopic composition of diamonds from popigai varies within the previously reported limits 13c 8 to 22 whereas diamonds from ebeliakh placers show heavier values of 13c 7 to 10 all the specimens studied contain very low amounts of n mostly 20 ppm but a few contained up to 60 ppm for specimens where the quantity of n allowed reliable analysis 15n values were found to be in the range of 3 9 to 11 9 on the basis of combined ar and n study it was concluded that impact diamonds studied here can be a mixture of at least two types of gas carriers e g different diamond components a possible explanation would be involvement of a carbon vapour deposition cvd process or diamond growth in the impact melt in addition to the direct graphite diamond shock transformation the 13c distributions and different n 36ar correlations have indicated a difference between impact diamonds from ebeliakh and diamonds extracted from popigai crater this could be explained by the existence of different diamond populations formed during the popigai impact event on the other hand ebeliakh diamonds could have resulted from a separate impact event to popigai and an alternative crater is yet to be found

constraining the internal variability of the stable isotopes of carbon and nitrogen within mantle diamonds the carbon and nitrogen isotope values of mantle xenoliths and xenocrysts are used to trace the cycling of volatiles in the deep earth for example to place empirical constraints on the origin of diamond forming carbon in the mantle the global database for diamond shows that the 13c value of peridotitic diamonds is very narrow typically around 5 whereas eclogitic diamonds can show positive and very negative 13c values resembling crustal carbonates and crustal organic carbon 2 commonly interpreted to reflect a relationship between eclogitic diamond formation and subduction zone planet tectonics curiously diamonds from both parageneses can show positive crust like and negative mantle like 15n values from 20 most of these data are derived from single stage combustion gas sourced mass spectrometry which produces simplistic datasets by fragmenting single diamonds or using in situ ion beam techniques it is known that single diamonds can show large scale heterogeneity for their carbon isotope values and nitrogen abundances sometimes as large as entire populations of diamond across a few hundred micrometres what is less well known is the scale of nitrogen isotope heterogeneity within single diamonds and if the nitrogen isotope heterogeneity of single diamonds can provide an insight into why diamonds that show very restricted 13c values show a much large range of 15n values to investigate the scale and to determine the origin of the nitrogen isotope heterogeneity source vs fractionation during diamond formation shown for populations of mantle diamonds we have determined multiple 13c 15n values and nitrogen abundances from 14 monocrystalline mcds and 25 polycrystalline diamonds pcds using step wise oxidation gas sourced mass spectrometry these data show that the heterogeneity shown for carbon and nitrogen isotope values from single diamond samples presented here is typically 5 and 8 respectively both of which are comparable to the standard deviation for the mean mantle 13c and 15n values 3 and 4 however there are samples that show much larger heterogeneities for 13c and 15n values 23 and 33 respectively which cannot be generated by equilibrium stable isotope fractionation during or prior to diamond formation these data suggest that isotopic heterogeneity may be present within the diamond forming fluid on sub mm scale or that these diamonds formed during multiple diamond formation events from isotopically distinct sources from these 39 samples there are only 5 pcds that show a larger range of carbon isotopes relative to nitrogen isotopes but of these 5 samples only 2 show a range of 13c values outside of analytical uncertainty the remaining 34 samples show a greater isotopic heterogeneity for 15n relative to 13c values the samples with the largest carbon and nitrogen isotopic heterogeneity are also the samples with low bulk 13c values 10 whilst there is no relationship between the ranges of nitrogen isotope values for a given sample and the corresponding bulk 15n value or nitrogen content these data show that 15n values recorded in mantle diamonds are relatively heterogeneous and can show both mantle like negative and crustal sedimentary like positive 15n values within the same sample we conclude that the large range of nitrogen isotope values seen within individual diamonds means that the observation of negative mantle like nitrogen in mantle diamonds acquired by single stage bulk combustion isotope ratio mass spectrometry cannot be used as a conclusive indicator for a mantle origin for the entirety of the diamond forming carbon and vice versa also the behaviour of 15n 14n is not coupled with the behaviour of 14n 12c during diamond formation instead it appears that diamond forming fluids can have positive and negative 15n values irrespective of their 13c value s these data suggest that subduction induced nitrogen isotope heterogeneity may not be coupled with subduction induced carbon isotope heterogeneity in diamond forming fluids

time space mapping of easter chain volcanism abstract new 40ar 39ar and published k ar ages show that the locus of volcanism along the easter volcanic chain evc has shifted systematically from the nazca ridge at about 26 m y to the recently active sala y gomez island easter island region this indicates a plume rather than a hotline i e mantle roll origin for the evc the time space distribution of ages combined with published ages for the galapagos and juan fernandez volcanic chains is used to reconstruct nazca plate velocities over the past 26 m y a plume now located in the region of sala y gomez island is most compatible with these data west of the plume the evc records neither nazca nor pacific plate motions this section of the evc may be related to westward channeling of plume material to the pacific nazca spreading boundary region

sea ice type maps from alaska synthetic aperture radar facility imagery an assessment synthetic aperture radar sar imagery received at the alaska sar facility is routinely and automatically classified on the geophysical processor system gps to create ice type maps we evaluated the wintertime performance of the gps classification algorithm by comparing ice type percentages from supervised classification with percentages from the algorithm the rms difference for multiyear ice is about 6 while the inconsistency in supervised classification is about 3 the algorithm separates first year from multiyear ice well although it sometimes fails to correctly classify new ice and open water owing to the wide distribution of backscatter for these classes our results imply a high degree of accuracy and consistency in the growing archive of multiyear and first year ice distribution maps these results have implications for heat and mass balance studies which are furthered by the ability to accurately characterize ice type distributions over a large part of the arctic

contrasted interactions between plume upper mantle and lithosphere foundation chain case 1 the foundation seamounts are a volcanic chain formed during the last 21 m y by the action of a hot spot presently located near the axis of the pacific antarctic ridge the western part of the chain is formed by volcanoes with ages ranging from 21 to 16 m y spatially distributed along two parallel lines roughly 200 km apart the shape and distribution of the edifices are strongly suggestive of an emplacement along preexisting fissures or fractures resulting from lithospheric deformation during the major kinematic reorganization of 25 m y their chemical and isotopic composition becomes enriched toward young volcano ages resulting from the progressive contamination of the upper mantle by the arrival of a plume pulse the eastern part of the chain is formed by volcanoes younger than 5 m y also distributed along two subparallel lines the distance between these two lines diminishes toward the pacific antarctic ridge axis a geoid high is located very near the pacific antarctic ridge axis over the volcanoes of the north line which lies in the prolongation of the older foundation seamounts and possibly marks the location of the foundation hot spot both the geoid anomaly and the morphology of the edifices show that the north line is the main locus of the volcanism the southern line was probably formed on top of the flexural arch resulting from the emplacement of the north line the chemical and isotopic compositions of the basalts reveal a growing influence of the ridge on the off axis plume magmatism the pattern is coherent with a mixing between two sources occurring when the two melting zones merge and overlap

volatile composition of microinclusions in diamonds from the panda kimberlite canada implications for chemical and isotopic heterogeneity in the mantle abstract in order to better investigate the compositions and the origins of fluids associated with diamond growth we have carried out combined noble gas he and ar c and n isotope k ca and halogen cl br i determinations on fragments of individual microinclusion bearing diamonds from the panda kimberlite north west territories canada the fluid concentrations of halogens and noble gases in panda diamonds are enriched by several orders of magnitude over typical upper mantle abundances however noble gas c and n isotopic ratios 3he 4he 4 6 ra 40ar 36ar 20 000 30 000 13c 4 5 to 6 9 and 15n 1 2 to 8 8 are within the worldwide range determined for fibrous diamonds and similar to the mid ocean ridge basalt morb source value the high 36ar content of the diamonds 1 10 9 cm3 g is at least an order of magnitude higher than any previously reported mantle sample and enables the 36ar content of the subcontinental lithospheric mantle to be estimated at 0 6 10 12 cm3 g again similar to estimates for the morb source three fluid types distinguished on the basis of ca k cl compositions are consistent with carbonatitic silicic and saline end members identified in previous studies of diamonds from worldwide sources these fluid end members also have distinct halogen ratios br cl and i cl the role of subducted seawater derived halogens originally invoked to explain some of the halogen ratio variations in diamonds is not considered an essential component in the formation of the fluids in contrast it is considered that large halogen fractionation of a primitive mantle ratio occurs during fluid melt partitioning in forming silicic fluids and during separation of an immiscible saline fluid

en echelon volcanic elongate ridges connecting intraplate foundation chain volcanism to the pacific antarctic spreading center abstract the development of volcanic elongate ridges vers could be controlled in many cases by complex processes related to interaction between mantle plumes and spreading centers we report here measured ages for the foundation chain se pacific showing that volcanism along morphologically distinct vers can develop occasionally as rapidly formed continuous lines of coeval volcanism extending from a region of intraplate volcanism to the pacific antarctic spreading center but a significantly more dominant trend is for coeval yet structurally disconnected segments of foundation chain vers to develop in a series of en echelon ne sw elongate zones of coeval hotspot volcanism these elongate zones developed at intervals of approximately 1 myr while maintaining a basically steady state orientation and size as the pacific antarctic spreading center migrated continually closer to the foundation plume hotspot we infer from this new information that foundation chain ver development was controlled by an interplay between short lived local factors e g location of nearest spreading center segment lithospheric stress and long lived attributes of the foundation plume hotspot e g size orientation periodicity

intraplate versus ridge volcanism on the pacific antarctic ridge near 37 s 111 w exploration of the foundation volcanic chain 33 s 131 w 37 s 111 w revealed the existence of different magmatic provinces with relation to their geological settings 1 the pacific antarctic ridge par is made up of several en echelon segments where both glassy midocean ridge basalts morbs with low incompatible elements k2o 150 ppm and ce 48 ppm at about 306 1300 km from the par axis 4 the old pacific seamounts built on a crust older than 23 m y located west of longitude 124 w 1300 km from the par axis consist of t and emorb on the par axis extensive crystal fractionation 65 produced the silicic lavas on the basis of pacific plate reconstruction using a half spreading rate of about 50 mm yr and integrating the observed compositional changes with respect to the structural settings it is inferred that the last volcanic events giving rise to the fs took place at about 110 km from the par axis about 5 m y ago the oblique ridges built between 5 m y and 23 m y with morb volcanics comparable to those of the the oblique ridge par provinces could also have been formed by an interaction between the foundation seamount dredge site 28 hotspot magmatism and that of an ancient accreting ridge magmatism precursor of the par

the carbonado diamond conundrum abstract the reviewer presents the results of a literature search on the enigmatic occurrences of carbonado a form but not the only form of polycrystalline diamond which is mined for industrial diamonds the principal occurrences are in brazil the central african republic car and siberia yakutia in the latter the name yakutite has been coined but though there are differences between these polycrystalline diamonds and the brazil car minerals they would seem to be little more significant than differences within the gondwana occurrences and yakutite should probably be regarded as another name for carbonado most occurrences are in placers and the minerals have probably been recycled more than once by sedimentary processes the ultimate source being unknown polycrystalline diamond has been described from the udachnaya pipe yakutia and though it is strictly framesite defined as an eruptive pipe variety of carbonado it differs little from other carbonados the fact that all occurrences known are in areas with kimberlites and gem diamond developments present suggests that carbonado does stem from terrestrial eruptive processes though not necessarily kimberlite pipes nevertheless this can be only a provisional personal conclusion there is much contradictory evidence in the literature the evidence of subjection to radiogenic agencies in car carbonados seems to be unexplained but it may be a secondary effect and not present in all carbonados this is a conundrum which still calls for much more research

are euhedral microdiamonds formed during ascent and decompression of kimberlite magma implications for use of microdiamonds in diamond grade estimation abstract the relationship between euhedral microdiamonds we propose an alternative hypothesis based on published experimental studies showing there is a significant decrease in the c bearing volatile content of kimberlite magma as pressure decreases during ascent of the kimberlite magma this may result in a pressure related transition from conditions at depth at which diamond is unstable in fluid undersaturated kimberlite magma to shallower level conditions at which diamond becomes stable or metastable as the magma reaches fluid saturation in this scenario macrodiamond xenocrysts of an early generation entrained at asthenospheric or deep lithospheric depths may partially or totally dissolve into the undersaturated magma upon disaggregation of their host rocks upon ascent of the magma to shallower depths and under appropriate oxidation conditions the lowered capacity of the magma to dissolve c bearing volatiles may result in euhedral microdiamond precipitation probably immediately before final eruption although framed in qualitative terms our hypothesis has testable consequences which we discuss in view of these considerations and the multiple possible relationships within and between microdiamonds and macrodiamonds in individual deposits we suggest that the use of microdiamond abundances from small samples as a guide to economic macrodiamond grade is problematic as an exploration strategy

laboratory measurements of sea ice connections to microwave remote sensing the connections between laboratory measurements and remote sensing observations of sea ice are explored the focus of this paper is on thin ice which is more easily simulated in a laboratory environment the authors summarize results of c band scatterometer measurements and discuss how they may help in the interpretation of remote sensing data they compare the measurements with observations of thin ice from ers and airborne radar data sets they suggest that laboratory backscatter signatures should serve as bounds on the interpretation of remote sensing data they examine these bounds from the perspective of thin ice signatures the effect of temperature and surface processes such as frost flowers and slush on these signatures controlled experiments also suggest new directions in remote sensing measurements the potential of polarimetric radar measurements in the retrieval of thickness of thin ice is discussed in addition to the radar results the authors discuss the importance of low frequency passive measurements with respect to the thickness of thin ice

the foundation seamounts tectonic setting of a newly discovered seamount chain in the south pacific abstract large areas of the south pacific remain unsurveyed because they are so remote a major volcanic chain the foundation seamounts lies between 33 s and 39 s and between 111 w and 125 w poorly defined on conventional bathymetric charts it becomes very apparent when combining an analysis of conventional geophysical data with the satellite altimeter data the length of the seamount chain is 1350 km and the volcanoes are clustered within a 180 km wide band trending approximately n70w which is the direction of absolute motion of the pacific plate over a fixed reference system some of these volcanoes are so shallow that they may have emerged above the sea surface at an earlier time no dates are known for the seamounts surrounding the foundation seamounts chain the tectonic setting is that of the pacific plate at the time when the strike of the spreading ridge changed from a northwesterly direction to the present northeasterly one this episode of spreading reorganization involved the existence of a short lived microplate west of the pacific antarctic ridge a captured segment of nazca plate accounts for the large discrepancies in the magnetic anomalies offsets along the agassiz fracture zone large propagators like the adventure and kurchatov troughs are described the newly discovered western segment of the chile fracture zone is the pacific plate match of the chile fracture zone on the nazca plate

ridge hotspot interaction the pacific antarctic ridge and the foundation seamounts the study of different magmatic provinces between the resolution fracture zone 33 s 131 w and the pacific antarctic ridge par axis 37 s 111 w suggests that similar processes of interaction between hotspot and spreading axial magmatism occurred 20 25 ma and 0 5 ma ago there is evidence of this process from the changes in composition observed in the lavas erupted near 400 300 km between the present day par axis 37 s 111 w and the eastern tip of the foundation seamount fs hotspot near 36 20 s 114 w where the last alkali enriched volcanics k ti 0 30 zr y 6 and ce yb n 4 have erupted this transitional province between the par and the fs consists of volcanic cones built on several volcanic ridges 20 ma also built on volcanic ridges are identified west 1200 km from the par axis of a failed rift propagator frp forming the eastern boundary of the ancient selkirk microplate some of these seamounts made of alkali basalts were built during the initiation of the fs hotspot 20 23 ma ago the interaction and the influence thermal of mantle plume magmatism with the ancient spreading ridge of the farallon pacific plates was responsible for the eruptions of the t morbs and andesitic lavas this situation is comparable to that presently observed on the par axis where silicic lavas are also erupted in association with t morbs

ion microprobe pb pb dating of carbonado polycrystalline diamond abstract we report in situ ion microprobe pb pb dating of quartz rutile and clay mineral inclusions and matrix part of polycrystalline diamonds carbonado derived from a proterozoic conglomerate in diamond bearing deposit of minas gerais in brazil together with u pb ages of zircons also extracted from the deposit thirty four spots on seven quartz grains located in the cavity of the gm01 carbonado yield 207pb 206pb isochron age of 3247 800 ma 2 mswd 0 75 and six spots on three rutile inclusions give the age of 3916 1300 ma 2 mswd 0 092 seven spots on three clay mineral inclusions of the do3 carbonado show common lead compositions while four spots on matrix define 207pb 206pb isochron age of 3811 1800 ma 2 mswd 0 012 seventy six spots on seventy zircon grains derived from the same conglomerate show three major u pb concordant ages of 2151 17 ma 2692 20 ma and 2931 22 ma with two concordant zircon outliers of 1726 58 ma and 3599 12 ma the youngest age is consistent with the formation age of 1750 1700 ma in the proterozoic conglomerate estimated by other workers the 3 6 ga zircon is the oldest record in the south american platform it may be detrital in origin and reflect the remnant of an archean craton the pb pb age of quartz and rutile inclusions in gm01 carbonado and that of do3 carbonado matrix are 3315 720 ma and 3811 1800 ma the matrix age is consistent with pb pb age of 2 6 3 8 ga of central african carbonados in the literature suggesting a close genetic relationship between brazilian and african carbonados

trade off in production between adjacent seamount chains near the east pacific rise bathymetric data and side scan sonar images collected near the southern east pacific rise between 15 and 19 s1 2 have revealed many seamounts on the west flank of the rise most of which are organized into chains running perpendicular to the rise axis the number of seamounts of 5 km diameter is at least twice that expected for average east pacific sea floor3 the formation of numerous small 5 myr linear seamount chains and the tendency for fresh lava flows to be found primarily at the near ridge ends of the chains suggest that there are plume like sources in the upper mantle which are relatively stationary active for extended periods and affected by adjacent sources

nitrogen aggregation in metamorphic diamonds from kazakhstan microdiamonds that occur in high grade metamorphic rocks of the kokchetav massif in kazakhstan have been interpreted as part of the metamorphic mineral assemblage implying previously unrecorded pressures for the metamorphism of crustal rocks analysis of the infrared and visible absorption spectra from kokchetav microdiamonds extracted from recent stream sediments draining the metamorphic rocks shows roughly 48 63 aggregation of single n substitution to a centres but no measurable further aggregation calculated residence times assuming peak metamorphic temperatures of 800 900 c are from 0 5 ma to 40 ma and support the petrographic evidence that these diamonds formed during the high pressure metamorphism rather than being inherited from premetamorphic sediments

backscatter characteristics of the winter ice cover in the beaufort sea the microwave backscatter statistics of the sea ice cover in the winter beaufort sea are characterized using c band synthetic aperture radar sar data collected by the european earth resources satellite 1 sea ice backscatter signatures were sampled from sar image data collected during the winter of 1991 1992 and winter of 1992 1993 the spatial and temporal variabilities of the backscatter signatures of different ice types are discussed the results show considerable seasonal stability of the backscatter signature of multiyear ice as well as of first year ice small amplitude regional variations of the multiyear ice backscatter can be observed consistent contrast between multiyear ice and first year ice is maintained throughout the season the highest radiometric variability is observed in sea ice in leads on the basis of these observations the backscatter from the principal ice types multiyear and first year are consistent with scatterometer observations and can be easily identified under winter conditions correlations of the regional variations of multiyear ice signatures to physical processes are suggested

he ar and c isotopes in coated and polycrystalline diamonds helium ar and c isotopic measurements have been undertaken on different qualities of industrial grade and polycrystalline diamond from localities in africa and brazil these include coated and cloudy diamonds which contain abundant volatile rich micro inclusions and framesites and carbonados which consist of aggregates of micron sized diamond crystals interspersed with mineral inclusions in an attempt to release selectively the primary trapped he from the diamonds they were analysed using an in vacuo crushing technique the he data are combined with ar k and u data obtained from 40ar 39ar stepped heating studies of irradiated fractions of the diamonds and bulk carbon isotope data obtained from the crushed residues results indicate that coated and cloudy diamonds best preserve a mantle signature with 3he 4he values of 1 7 ra and 13c of 5 to 6 coated diamonds have uniformly high he and ar concentrations of 10 6 10 5 cm3 g 1 framesites have lower 3he 4he values 0 1 3 ra and bimodal 13c values with modes at 6 and 20 carbonados show both the lowest 13c values 25 and 3he 4he of 0 1 ra u and k concentrations show a progressive increase from coats framesites carbonados while it is tempting to attribute low 13c low 3he 4he and high u to the influence of subducted crustal material it is likely that implantation of 4he by u th rich minerals adjacent to the micro diamonds is also a possible cause of the low he isotope ratios

geochemical consequences of intense pulse like degassing during the onset of the central atlantic magmatic province the triassic jurassic boundary tjb ismarked by one of the five largestmass extinctions of the phanerozoic and the eruption of a large igneous province the central atlanticmagmatic province camp the tjb is characterized by a carbonate production crisis by negative excursions in the carbon isotopic ratio of buried organic matter and by successive peaks in atmospheric co2 herewe use the numerical model geoclimto explore the possible connections between the camp emplacement and the observed carbon cycle perturbations different degassing scenarios linked to the camp eruption are explored we show that the emission of realistic amounts of co2 that follow a geologically constrained degassing scenario as short termpeaks less than 10 ka leads to successive decrease in carbonate production as observed in the geological record we also calculate the evolution of carbon isotopes and show that our model reproduces the amplitude of the isotopic excursion with a volcanic degassing of co2 characterized by a carbon isotopic composition of 20 such low values could be associated to carbon pools of light isotopic composition located at the transition zone cartigny p 2010 earth and planetary science letters v 296 p 329 339 and not necessarily to biogenicmethane release finally themodel predicts a succession of short term co2 rises with an amplitude in close agreement with available proxy based reconstructions

piston core record of late paleogene 31 ma to recent seafloor hydrothermal activity in the southwest pacific basin a large diameter piston core containing 8 35 m of metalliferous sediment has been recovered from a small abyssal valley in the remote southwest pacific basin 31 42 194 s 143 30 331 w 5082 m water depth providing unique insight into hydrothermal activity and eolian sedimentation there since the early oligocene a combination of fish teeth sr isotope stratigraphy and inaa geochemical data reveals an exponentially decreasing hydrothermal flux 31 ma to the present although hydrothermal sedimentation related to seafloor spreading explains this trend a complex history of late eocene early oligocene ridge jumps propagating rifts and plate tectonic reorganization of south pacific seafloor could have also played a role a possible hiatus in deposition as recorded by changes in core composition just below 2 m depth is beyond the resolution of the fish teeth sr isotope dating method employed here however the timing of this interval may be coincident with extinction of the pacific farallon ridge at 20 ma a low flux eolian component accumulating at this site shows an increase relative to the hydrothermal component above 2 m depth consistent with dust generating continental sources far to the west australia new zealand this is the first long term paleoceanographic record obtained from within the south pacific bare zone rea et al 2006 an anomalous region where pacific seafloor has largely escaped sediment accumulation since the late cretaceous

new insight into polycrystalline diamond genesis from modern nanoanalytical techniques abstract technical developments in analytical methods that reach nanometer spatial resolution have enabled the interrogation of smaller submicron sized inclusions in diamond that had previously been elusive this has inspired and enabled studies of non classical diamond species from different geological settings resulting in a strongly faceted and dynamic picture of diamond formation this article reviews the leap of knowledge achieved by employing state of the art analytical methods with high spatial resolution to polycrystalline diamonds from different settings i e from kimberlite from crustal ultra high pressure metamorphic terranes and alluvial carbonados while crustal metamorphic diamonds are generally formed under oxidizing conditions polycrystalline diamond from the earth s mantle and carbonado have inclusion suites reflecting variable and sometimes extreme redox conditions diamond fluid compositions however fall in the same compositional field for worldwide diamond fluids regardless of their geodynamic environment on the basis of thermodynamic equilibrium data for c h o fluids in the mantle we argue that submicron inclusions in diamonds are products of local remobilization connected to fluid fluxed partial melting and redox freezing thus evidence from these inclusions complements information from classical work on larger inclusions and allows a unique direct insight into the medium in which diamond formed

comprehensive analysis of nanodiamond evidence relating to the younger dryas impact hypothesis during the end of the last glacial period in the northern hemisphere near 12 9k cal a bp deglacial warming of the bolling allerod interstadial ceased abruptly and the climate returned to glacial conditions for an interval of about 1300 years known as the younger dryas stadial the younger dryas impact hypothesis proposes that the onset of the younger dryas climate reversal pleistocene megafaunal extinctions and disappearance of the clovis paleoindian lithic technology were coeval and caused by continent wide catastrophic effects of impact bolide events in north america while there are no known impact structures dated to the younger dryas onset physical evidence of the impact bolide events is argued to be present in sediments spanning several continents at stratigraphic levels inferred to date to the bolling allerod younger dryas boundary ydb reports of nanometer to submicron sized diamonds in ydb sediments in particular the rare 2h hexagonal polytype of diamond lonsdaleite have been presented as strong evidence for shock processing of crustal materials we review the available data on diamonds in sediments and provide new data we find no evidence for lonsdaleite in ydb sediments and find no evidence of a spike in nanodiamond concentration at the ydb layer to support the impact hypothesis

evaluation of second order texture parameters for sea ice classification from radar images with the advent of airborne and spaceborne synthetic aperture radar sar systems sea ice classification from sar images has become an important research subject since gray tone alone has proven to be of limited capability in differentiating ice types texture has naturally become an attractive avenue to explore accordingly performance of texture quantification parameters as related to their ability to discriminate ice types has to be examined sar image appearance depends on radar parameters involved in the image construction procedures from the doppler history record therefore the feasibility of using universal texture ice type relationships that hold for all combinations of radar parameters also has to be investigated to that end imagery data from three different sar systems were used in this study five conventional texture parameters derived from the gray level co occurrence matrix glcm were examined two of them were modified to ensure their invariant character under linear gray tone transformations results indicated that all parameters were highly correlated the parameters did not in general vary with the computational variables used in generating co occurrence matrices ice types can be identified uniquely by the mean value of any texture parameter the relatively high variability of texture parameters however confuses ice discrimination particularly of smoother ice types ice classification was conducted using a per pixel maximum likelihood supervised scheme when texture was combined with gray tone the overall average classification accuracy was improved texture was successful in improving the classification accuracy of multiyear ice but was less promising in discriminating first season ice types the best two glcm texture parameters according to the computed overall average classification accuracies were the inverse difference moment and the entropy a brief description of glcm texture parameters as related to ice s physical characteristics is presented

aspects of diamond mineralisation and distribution at the helam mine south africa abstract the diamonds from the swartruggens dyke swarm are mainly tetrahexahedra with subsidiary octahedral and cuboid crystals they are predominantly colourless with subordinate yellows browns and greens the existence of discrete cores and oscillatory growth structures within the diamonds together with the recognition of harzburgite lherzolite at least two eclogitic and a websteritic diamond paragenesis variable nitrogen contents and both type iaab and type ib iaa diamonds provides evidence for episodic diamond growth in at least six different environments the predominance of plastic deformation in the diamonds the state of nitrogen aggregation and the suite of inclusion minerals recovered are all consistent with a xenocrystic origin for the diamonds with the type ib iaa diamonds being much younger than the rest mantle storage at a time averaged temperature of 1100 c is inferred for the type iaab diamonds the distribution of mantle xenocrysts of garnet and chromite within the high grade main kimberlite dyke compared to the low grade changehouse kimberlite dyke strongly suggests that the difference in diamond content is due to an increased eclogitic component of diamonds in the main kimberlite dyke

evidence of fluid inclusions in metamorphic microdiamonds from the kokchetav massif northern kazakhstan abstract microdiamonds from garnet clinopyroxenites of the kokchetav massif northern kazakhstan and associated alluvial diamonds have been investigated using infrared spectroscopy all diamonds have high nitrogen contents from 747 up to 4488 20 at ppm and are of type ib iaa nitrogen data are consistent with a diamond formation over a narrow temperature range microdiamonds from garnet clinopyroxenites are characterized by water and carbonate inclusions similar to those ocurring in fibrous coated diamonds from kimberlite which suggest that diamonds grew from a c h o fluid in contrast alluvial microdiamonds do not contain any carbonate inclusions and h2o is absent or present in only minor amounts alluvial diamonds are considerably more n rich but have a similar range of nitrogen aggregation states it is suggested that alluvial diamonds belong to a separate diamond population compared with the microdiamonds from garnet clinopyroxenites the kokchetav microdiamonds are distinct from kimberlitic fibrous diamonds in that they contain abundant ib centres have high nitrogen contents and show different populations depending on host rock type these characteristics support a metamorphic origin for the microdiamonds from the uhpm rocks of the kokchetav massif

migration rate of volcanism along the foundation chain se pacific abstract volcanism has migrated along the nw se trending foundation chain se pacific at a rate of 91 2 mm y for the past 21 million years my the foundation chain is at least 1900 km long and was erupted mostly in the interior of the pacific plate the linear migration of intraplate often geochemically enriched volcanism along the foundation chain can be explained by the theory of tectonic plate drift over a narrow stationary plume of hot mantle material upwelling from depth the present hotspot or at least its eastern extent generated by this foundation plume is now located on or close to the pacific antarctic spreading axis local spreading microplate boundaries have migrated systematically towards the foundation plume for at least the past 21 my a process that was however interrupted by the creation of the selkirk microplate the foundation chain has erupted therefore onto ocean crust ranging in age from 17 ma to 0 ma with distances between the foundation plume and local spreading microplate boundaries varying from 900 km to 0 km such interplay between the foundation plume and local seafloor spreading and microplate boundaries probably in combination with changing stresses in the lithosphere apparently induced major changes in the fabric and composition of the foundation chain e g the switch from individual seamounts to elongated en echelon ridges at 5 ma it can also explain why ages for a few foundation seamounts located at the edges of the selkirk microplate do not lie along the overall linear trend of migrating volcanism the linear velocity of the pacific plate over the foundation plume calculated on the basis of the migration rate of volcanism along the foundation chain is predicted by a number of rotation poles for the motion of the pacific plate in a fixed hotspot reference frame the fact that the measured migration rates of volcanism along the foundation and hawaiian chains are predicted by these rotation poles 1 confirms that the distribution of foundation chain ages records the absolute motion of the pacific plate and 2 supports the fundamental assumption of stationary mantle plumes in the case of hawaii versus foundation for at least the past 21 my the foundation chain was created by a weak plume primarily as relatively small probably rapidly erupted 1 my individual seamounts or seamount clusters at a rate of approximately one every my linear migration rates of volcanism are most likely defined unequivocally along such types of hotspot chain on the basis of age distance data it should also be easier to identify and characterize volcanism created as a result of plume interactions with local spreading microplate boundaries rotation poles for pacific plate drift show that the initial stages of volcanism along the southern austral chain 34 ma could have been created by the foundation plume suggesting that the path of pacific plate drift over the stationary foundation plume could be at least 3000 km long

the origin and formation of metamorphic microdiamonds from the kokchetav massif kazakhstan a nitrogen and carbon isotopic study abstract this study reports 13c 15n and n content values for microdiamonds from ultrahigh pressure metamorphic rocks of the kokchetav massif in kazakhstan both alluvial diamonds and in situ diamonds from a garnet clinopyroxene rock and a marble i e a garnet pyroxene dolomitic rock were investigated in situ diamonds were analysed in batches because of their small size average 40 m whereas the larger alluvial diamonds were analysed individually the latter group has 13c values ranging from 15 92 to 10 57 15n from 1 8 to 1 1 and n contents from 2300 to 3650 ppm diamonds from the garnet clinopyroxene rock yield mean values of 10 50 for 13c 5 9 for 15n and a high average nitrogen content of 11 150 ppm values for diamonds in marble are 10 19 8 5 and 2650 ppm respectively for diamonds from garnet clinopyroxene rock and marble there is more nitrogen released by bulk combustion than estimated by infrared ir spectroscopy the differences being of about 7000 and 1500 ppm respectively these differences suggest that a significant quantity of nitrogen is ir inactive and may be present as fluid inclusions their carbon and nitrogen isotopic compositions are compatible with an in situ crystallisation of diamond from dominantly metasedimentary sources suggesting that sedimentary nitrogen can be subducted to very high pressures carbon isotopic fractionation between coexisting carbonate and diamond suggests crystallisation temperatures before the peak of metamorphism at temperatures probably below 700 c and deduced pressures of 3 gpa relative to the isotopic data reported for sediments metasediments and in situ diamonds the slightly 15n depleted compositions of alluvial diamonds is striking these values suggest that the contribution of any metasedimentary source is unlikely and may point toward a mafic ultramafic protolith

komatiites i eruption and flow because of their high eruption temperatures and ultrabasic composition komatiite lavas had low viscosities which typically ranged from 0 1 to 10 pa s a major consequence of this low viscosity is that most lavas erupted as turbulent flows an analysis of their ascent through the lithosphere suggests ascent velocities in the range of 1 to over 10ms 1 and reynolds numbers much greater than the critical value of 2000 the lavas would have remained turbulent for most or all of their subsequent flow and emplacement typical horizontal flow rates are estimated to range from 0 5 to 100 m2 s per unit width of flow such turbulent lava flows would have lost their heat by convection to the surroundings at rates which are orders of magnitude greater than the rates for laminar flows which cool by conduction a quantitative analysis of the cooling of komatiites indicates cooling rates from over 1000 c hr to a few c hr 1 while the flows remained turbulent these rates are in an appropriate range to cause phenomena such as high nucleation rates strong supersaturation of the lava delayed nucleation of olivine and skeletal or dendritic crystal morphologies komatiites often flowed over ground composed of rocks with lower melting temperatures it is proposed that the turbulent lavas melted the ground to form deep thermal erosion channels melting rates at the lava source are calculated at several metres per day and deep troughs with depths of several metres to hundreds of metres and lengths of several kilometres probably formed laboratory experiments performed to simulate thermal erosion show qualitative agreement with the theory with channel depth decreasing downstream the experiments also revealed that the channel margins become undercut during thermal erosion to form overhanging sides of the channel some sinuous rilles observed in the mare regions of the moon are thought to have formed by thermal erosion hulme 1973 they provide analogues of the channels postulated to form in komatiite eruptions where conditions were in fact more favourable for thermal erosion an assessment of the role of olivine crystals precipitated in the cooling turbulent flows indicates that they will remain in suspension until the lava has come to rest contamination of komatiite lava by underlying rock can be as much as 10 per cent some illustrative calculations show how the major element and trace element compositions of residual melts can be significantly modified by combined assimilation and fractional crystallization in a moving flow assimilation of tholeiitic basalt into a komatiite can cause incompatible trace element ratios such as ti zr and y zr and the rare earth patterns of derivative lavas to vary substantially some of the variations in such geochemical parameters which are often ascribed to mantle heterogeneity also could have resulted from assimilation of the ground assimilation could have modified the isotope geochemistry of lava suites and led to apparent ages which differ from the true eruption age the thermal erosion model also provides an explanation of the formation of some nickel sulphide ores found at the bottom of thick komatiite flows it is proposed that ores can form by assimilation of sulphur rich sediment which combines with ni from the komatiite to form an immiscible liquid

the pacific antarctic ridge foundation hotspot interaction a case study of a ridge approaching a hotspot the foundation hotspot pacific antarctic ridge par system is the best documented case of a fast spreading ridge approaching a hotspot and interacting with it the morphology crustal structure inferred from gravity anomalies and the chemical composition of the lavas of the axial area of the par show evidence of the influence of the hotspot that is presently located roughly 35 km west of the spreading ridge axis along axis variation in the mantle bouguer anomaly is about 28 mgal corresponding to a crustal thickening of 1 5 km where the hotspot is nearer to the par anomalous ridge elevation is 650 m and the along axis width of the chemical anomaly is 200 km a comparison of these axial parameters with those derived for other ridge hotspot systems suggests that the amount of plume material reaching the ridge axis is smaller for the foundation par system this implies a weaker connection between the plume and the ridge cumulative effects of a fast spreading rate and of a fast ridge hotspot relative motion can be responsible for this weak plume ridge flow the flow from the hotspot may be less efficiently channelled towards the ridge axis when a fast ridge is rapidly moving towards a hotspot

carbonado physical and chemical properties a critical evaluation of proposed origins and a revised genetic model abstract carbonado diamond is the most controversial of all diamond types and is found only in brazil and the central african republic bangui neither an affinity to earth s mantle nor an origin in the crust can be unequivocally established carbonado diamond is at least 3 8 ga old an age about 0 5 ga older than the oldest diamonds yet reported in kimberlites and lamproites on earth derived from neo to mid proterozoic meta conglomerates the primary magmatic host rock has not been identified discovered in 1841 the material is polycrystalline robust and coke like and is best described as a strongly bonded micro diamond ceramic it is characteristically porous which precludes an origin at high pressures and high temperatures in earth s deep interior yet it is also typically patinated with a glass like surface that resembles melting with exotic inclusions of highly reduced metals carbides and nitrides the origin of carbonado diamond is made even more challenging but the challenge is important because a new diamondiferous host rock may be involved and the development of a new physical process for generating diamond is possibly assured the combination of micro crystals and random crystal orientation leads to extreme mechanical toughness and a predicable super hardness the physical and chemical properties of carbonado are described with a view to the development of a mimetic strategy to synthesize carbonado and to duplicate its extreme toughness and super hardness textural variations are described with an emphasis on melt like surface features not previously discussed in the literature but having a very clear bearing on the history and genesis of carbonado selected physical properties are presented and the proposed origins diverse in character and imaginatively novel are critically reviewed from our present knowledge of the dynamic earth all indications are that carbonado is unlikely to be of terrestrial origin a revised model for the origin of carbonado is developed based on 1 new observations which show that white dwarf stars can have diamond cores 2 c rich exoplanets may have diamond bearing mantles and 3 new shock wave experiments on methane suggest that diamond may be present in large gaseous planets such as saturn uranus and neptune where diamond in the core is solid and in jupiter where liquid diamond may be present it is proposed that carbonado diamond was delivered to earth from extra solar sources during the episode of late heavy bombardment 4 1 3 8 ga if the currently held view that r process heavy elements were added as a late veneer to earth through the collision of white dwarfs in kilonova explosions then why not carbonado diamond during this epic event

a carbon and nitrogen isotope study of diamond from primitive chondrites diamonds isolated from primitive chondrites of the carbonaceous ordinary and enstatite groups have been analysed by high resolution stepped combustion followed by measurement of their c and n isotopes using a newly adapted technique that allows quantitative measurements of c n ratios the 13c of the diamond is shown to vary between meteorite groups from 32 to 38 0 and the measured c n ratios suggest that the n concentration of diamond ranges over a factor of 7 from 1800 ppm tieschitz to 13 000 ppm adrar 003 the 15n of n released from diamond is constrained to 348 7 the complexity of the c release pattern and c n ratio during combustion implies the presence of more than one component which suggests that either more than one type of diamond is present in the samples or unidentified additional phases are located in the acid resistant residue the components are present in varying proportions between meteorite groups the data are compatible with a model of a mix of different diamond populations some probably presolar and some possibly solar existing in the early solar nebula where each population originally contributed a roughly equal amount to chondrites of every class subsequent metamorphism has resulted in overall variations in 13c and c n ratios in diamond isolated from meteorites of differing petrologic grade without significantly altering the n isotopic composition possible ways for this to be achieved are explored

chemical heterogeneity in carbonado an enigmatic polycrystalline diamond abstract carbonado a polycrystalline variety of diamond is characterized by unusual carbon isotope compositions with bulk 13c values clustered tightly between 23 and 30 relative to pdb these values are significantly lighter than harzburgitic diamond with a range in 13c from 1 to 10 and fall near the lower extreme for eclogitic diamond ranging from 3 to 34 in combination with textural and inclusion data these isotopic compositions have led scientists to question whether carbonado originated in the mantle or in the crust previous studies of carbonado have revealed a bimodal grain size distribution that correlates with cathodoluminescence cl emissions we believe that these textures result from a two step growth process and we have obtained additional chemical evidence that supports the identification of two distinct crystal populations ion microprobe analyses of a central african carbonado reveal a bimodal distribution of 13c values of 24 and 26 with an instrumental precision of 0 29 secondary ion mass spectrometry analyses also demonstrate that this 13c distribution coincides with variations in nitrogen abundance and both of these chemical zonations correlate with cl emission signatures a one dimensional analysis of self diffusion of carbon in diamond suggests that isotopic homogenization occurs extremely slowly even under upper mantle conditions whereas the microscale distribution of carbon isotopes in carbonado does not constrain the temperature pressure or time of carbonado formation it does provide a geochemical signature that recorded the dynamics of the growth process

early proterozoic ultrahigh pressure metamorphism evidence from microdiamonds microdiamonds from the akluil k minette dykes nunavut canada are similar to diamonds formed in subducted metamorphic rocks high concentrations of unaggregated nitrogen and positive 15 n suggest that the microdiamonds formed within rocks subducted to ultrahigh pressures before being sampled by the minette magma 1 8 billion years ago this ultrahigh pressure metamorphism in north america probably related to the trans hudson orogen about 2 billion years ago extends the occurrence of ultrahigh pressure metamorphism from 0 6 billion years to before 1 8 billion years ago and suggests that phanerozoic type subductions were active by the early proterozoic

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

morphostructural study and type of volcanism of submarine volcanoes over the pitcairn hot spot in the south pacific undersea volcanoes found at about 80 km southeast of the island of pitcairn are believed to be the manifestation of a hot spot activity located near 129 30 w 25 10 s along the strike of the mururoa gambier pitcairn volcanic alignment hydrothermal activities and recent volcanic flows were observed on the two largest 20 km in basal diameter and shallowest 60 m and 450 m depth volcanoes more than twenty other smaller volcanic edifices 0 25 made up of ancient morb type tholeiitic rocks are inferred to be inherited from the epr axial regions the shallow volcanic activity which occurred on the two largest edifices are classified as 1 reactive eruptions with hydromagmatic activities giving rise to volcanic ejecta bombs xenoliths and ash and 2 quiet eruptions which formed pillows and or lobated lavas and large massive flows intrusives dyke and sill were observed cutting through the volcanic ejecta near the summit 500 m depth of the seamounts the general structural orientations of the rift zones recognized from the bathymetry of individual volcanoes n160 180 n80 n30 and n120 are comparable to those observed in the society and austral hot spot regions these orientations were inferred as corresponding to the structural discontinuities of the ancient oceanic crust and to the regional stress field of the pacific plate rock samples from the pitcairn region consist of alkali basalts basanites trachyandesites and trachytes which are closer in chemical composition to some of the volcanics from the society rather than to those from the austral hot spot regions

carbon isotope fractionation during experimental crystallisation of diamond from carbonate fluid at mantle conditions we report first results of a systematic study of carbon isotope fractionation in a carbonate fluid system under mantle pt conditions the system models a diamond forming alkaline carbonate fluid using pure sodium oxalate na2c2o4 as the starting material which decomposes to carbonate co2 and elementary carbon graphite and diamond involving a single source of carbon following the reaction 2na2c2o4 2na2co3 co2 c near liquidus behaviour of carbonate was observed at 1300 c and 6 3 gpa the experimentally determined isotope fractionation between the components of the system in the temperature range from 1300 to 1700 c at 6 3 and 7 5 gpa fit the theoretical expectations well carbon isotope fractionation associated with diamond crystallisation from the carbonate fluid at 7 5 gpa decreases with an increase in temperature from 2 7 to 1 6 this trend corresponds to the function carbonate fluid diamond 7 38 106 t 2

a 220 km2 recently erupted lava field on the east pacific rise near lat 8 s seamarc ii records show a 220 km2 area of unusually high reflectivity on the east pacific rise epr near lat 8 s which we interpret to be a recently erupted lava field this is the only segment of the epr exhibiting high reflectivity over such a large area in our continuous seamarc ii coverage from lat 8 n to 18 n and 3 s to 23 s the lavas appear to issue from the axial neovolcanic zone between lat 8 15 and 8 17 s the lava field extends up to 18km off axis and inundates scarps up to 100 m high on the basis of measurements of scarp heights just outside areas where they are buried we estimate the average thickness of the field to be 70 20 m thus the volume of the lava field is 15 4 km3 in comparison the average annual volcanic budget for the earth is approximately 4 5 km3 and the largest historic basaltic eruption from the icelandic laki fissure in 1783 was approximately 12 3 km3 when did the eruption occur comparative studies of acoustic reflectivity and photographed bottom characteristics elsewhere along the epr suggest that the lava field has little or no sediment cover and is very young this is also one of the only areas on the epr where earthquakes occur that do not appear to be caused by transform faulting if the earthquakes are related to the lava field then major eruptions may have occurred in 1964 1965 and 1969 a large helium plume near lat 13 s may be caused in part by eruptions of the lat 8 s lava field this is consistent with estimates of currents at 2 3 km depth which are such that a plume generated at lat 8 s would eventually appear off axis at lat 13 s our observations suggest that this spreading segment which is bounded by small ridge axis discontinuities at lat 8 05 s and 8 47 s may have been the most volcanically active segment along the epr during the past 25 yr

dual polarization c band radar observations of sea ice in the amundsen gulf polarimetric observations of sea ice from synthetic aperture radar can in principle assist in sea ice classification and ice water discrimination in this paper we use dual polarization ground based scatterometer observations of sea ice to assess the potential value of spaceborne dual polarization observations of sea ice for operational ice analysis focusing on c band and in particular the contribution of the hv backscatter coefficient and hh vv polarization ratios results show that signature variability resulting from frost flowers ice deformation and snow cover can overwhelm systematic differences between younger ice types up to first year thin as a result of this and noise floor limitations of spaceborne sensors the hv backscatter coefficient makes visual ice type and open water discrimination easier only below about 30 incidence angle the hh vv ratio is less impacted by the noise floor of spaceborne sensors but retains similar ambiguities for sea ice classification

geomorphology and structural segmentation of the crest of the southern pacific antarctic east pacific rise geomorphology of the boundary between pacific and antarctic plates was mapped with a sea beam multibeam echosounder and a seamarc ii bathymetric side scan sonar from the southern end of juan fernandez microplate at 35 s to heezen transform at 56 s there are six spreading center systems separated by two large left stepping nontransform offsets at 36 5 s and 41 5 s two right stepping transform fault systems and a left stepping hybrid structure with equally long strike slip and nontransform offsets axial rift zones spreading axes are generally within 1 of normal to the relative motion predicted by current plate rotation models most axial rift zones crop out along the crests of typical east pacific rise epr axial ridges which commonly have flat rather than humped long profiles about 2 of this fast spreading 84 100 mm yr rise crest has an axial rift valley instead of an axial ridge the longest rift valley segment is midway between menard and vacquier transforms near 51 s where an anomalously deep rise crest may mark a zone of below average mantle upwelling nontransform offsets structurally similar to those on the tropical epr but mostly formed by differential asymmetric spreading subdivide the four longest spreading center systems on the northern transform free two thirds of the rise net rift propagation at migrating offsets has been into the faster pacific plate this causes right steps to migrate north left steps to migrate south and crust to be transferred to the east flank this pattern has prevailed for several million years judging from the oblique fracture zones pseudofaults mapped on the rise flanks with older marine data and geosat altimetry on this rise crest the difference in stress on two plates with very different velocities may control the direction of offset migration

diamonds from the popigai impact structure russia diamonds were found in impact melt rocks and breccias at the popigai impact structure in siberia the diamonds preserve the crystallographic habit and twinning of graphites in the preimpact target rocks from which they formed by shock transformation secondary and transmission electron microscopy indicate that the samples are polycrystalline and contain abundant very thin lamellae which could represent stacking faults with local hexagonal symmetry or microtwins microcrystalline units are 1 m infrared spectroscopy indicates the presence of solid co 2 and water in microinclusions in the diamonds co 2 being under a pressure greater than 5 gpa at room temperature trace element and isotopic compositions confirm the derivation from graphite precursors

the foundation seamount chain a first survey and sampling the foundation seamounts form a 1400 km long chain on the pacific plate from 32 s 127 w to the pacific antarctic spreading axis at 38 s 111 w previously only known from sparse single beam echosoundings and satellite altimetry we present here the first multibeam bathymetric survey and geological sampling results we confirm that the submarine topography correlates with the altimetry and that the chain is volcanic rather than tectonic or microcontinental in origin the chain can be divided up morphologically and geochemically into three section 1 west of 125 w large flat topped volcanoes composed of incompatible element depleted lavas 1 of a near ridge origin with little or no plume influence 2 between 125 and 115 w true intraplate volcanoes with incompatible element enrichment 1 9 generated over the foundation plume 3 east of 115 w e w trending volcanic ridges with compositions 2 0 0 3 suggestive of interaction between the plume and the pacific antarctic spreading axis on the spreading axis moderate incompatible element enrichments 0 8 cf 0 3 outside the foundation area also suggest plume influence it appears that the activity of the foundation plume in the last few million years has 1 significantly waned and 2 become wholly channeled towards the spreading axis the foundation plume may be in the process of dying

mantle related carbonados geochemical insights from diamonds from the dachine komatiite french guiana abstract carbonado is a unique type of polycrystalline diamond characterised among others by 13c depleted isotope compositions 13c 25 vs pdb little advanced nitrogen aggregation ib iaa and sintered ceramic like diamond grains its origin remains an enigma with models proposing a formation either in the earth s crust or even within an exploding super nova the possibility that carbonado formed in the earth s mantle is often rejected because diamond with carbonado like geochemical features has never been found in rocks such as kimberlites that carry diamonds from the mantle in this study it is shown that the c and n stable isotope compositions nitrogen contents and nitrogen speciation of diamonds from the dachine komatiite french guyana exhibit unambiguous similarities with carbonados these include c isotopes from 32 6 to 0 15 mode at 27 n aggregation only ib iaa diamonds from 2 to 76 of n pairs and n isotopes from 4 1 to 6 9 average 2 1 2 9 which all strikingly match the carbonado data this evidence illustrates that the main geochemical arguments usually called to reject a mantle origin of carbonado are no longer valid a model linking carbonado crystallisation from komatiite volatiles is developed in this model the sintering is produced by the high temperature of the komatiite magma thus accounting for their absence in colder kimberlites the low 13c compositions of carbonados would be inherited from the transition zone 300 km depths which is known to yield diamonds with distinct c isotope distributions compared to most lithospheric diamonds 150 300 km depths this model can account for most available observations of carbonados including their large size sintering photoluminescense cathodoluminescence features and geochemical characteristics