nitrogen and carbon isotopic composition in the diamonds of mbuji mayi zaire the concentration and isotopic composition of nitrogen measured in large diamonds gram size from the mbuji mayi kimberlite district zaire show a large range of variation 100 n 2100 ppm 11 2 15n 6 0 the15n depleted nitrogen is associated with the higher nitrogen concentrations the large diamonds are individually rather homogeneous in13c range of 13c 0 9 while variations occur within small octahedral diamonds from the same district range up to 5 8 the total range of 13c variation is about the same for the large diamonds 10 5 13c 5 5 the small octahedral diamonds 10 13c 4 6 and the carbonates from local kimberlites 11 8 13c 5 5 the diamond carbon isotopic data could indicate a complex story of crystallization within a deep seated system fractionating its carbon isotopes the nitrogen results indicate that nitrogen in diamonds is on the average markedly depleted in15n weighted average 5 15 relative to atmosphere sediments and upper mantle

ammonium partitioning and nitrogen isotope fractionation among coexisting micas during high temperature fluid rock interactions examples from the new england appalachians abstract despite recent advances in the field of n isotope geochemistry our understanding of the behavior of this element in the solid earth remains limited by a lack of fundamental information regarding the partitioning of ammonium and isotopic fractionation of n among coexisting mineral and fluid phases study of n behavior in regionally metamorphosed rocks provides the opportunity to assess intermineral nh 4 partitioning and n isotope fractionation among coexisting micas during metamorphism and affords an application of the n system as a tracer of high t fluid rock interactions analyzed mica samples range in 15 n air from 3 3 to 11 9 and contain 9 to 1820 ppm n the outcrop at townshend dam vermont allows examination of n behavior across strike on a relatively small scale and samples from western maine demonstrate the effect of varying metamorphic conditions on n behavior in metapelites 15 n bt w mica 15 n biotite 15 n white mica ranges from 0 9 to 2 7 for all samples from both suites mean 0 36 with 1 0 79 with samples containing a separate paragonite white mica phase showing the greatest range 0 12 to 1 02 mean 0 58 1 1 03 thirteen samples containing only na poor muscovite six from townshend dam seven from western maine have mean 15 n bt w mica of 0 07 1 0 41 in both suites biotite nearly always contains more n than coexisting white mica but n w mica n bt also shows some significant scatter mean n w mica n bt 0 46 with 1 0 34 the thirteen samples containing only a na poor muscovitic white mica phase have mean n w mica n bt 0 39 with 1 0 26 similar to that reported by others for other metamorphic suites containing only muscovite as the white mica phase there is no obvious suggestion of equilibrium n isotopic fractionation among coexisting micas at epidote amphibolite to amphibolite facies metamorphic conditions although nh 4 appears to partition systematically among coexisting biotite and white mica significant scatter in both 15 n bt w mica and nh 4 partitioning conceivably the result of differential closure to exchange during cooling or of retrograde replacements could however obscure observation of small equilibrium intermica fractionations related to the characteristics of the interlayer sites in which nh 4 resides samples most unlike the mean in both 15 n bt w mica and n w mica n bt contain abundant chlorite some of which is likely retrograde based on petrographic observations chl chl bt 0 3 thus retrograde replacement of biotite by chlorite may have been accompanied by fluid mineral n isotope exchange perhaps involving the production of fine grained retrograde n bearing white mica observed petrographically for some samples it is also possible that sampling at scales greater than those of n isotope equilibrium domains e g across fine interlayers results in some scatter because of varying relative modal proportions of the two micas in adjacent fine interlayers although further investigation of the extent of retrograde reequilibration of mica n systematics is warranted the observed lack of systematic n isotope fractionation among coexisting micas and the reasonably systematic nh 4 partitioning data for these phases provide important preliminary constraints for attempts to model n isotope behavior in fluid rock systems these results and other attempts to calibrate n isotope fractionation through field studies point to the conspicuous lack of experimentally determined mica fluid n isotope fractionation factors

a balanced section across the pyrenean orogenic belt evolutionary models that have been proposed for the pyrenean orogenic belt involve gravitational gliding of major thrust sheets to both the north and south of an uplifted central axial zone it has been suggested by previous workers that uplift is a result of alpine compression or long lived strike slip movement on the north pyrenean fault we critically assess these models and propose a new model based on the generation of a thin skinned linked thrust system due to alpine collision of iberia and europe pyrenean alpine tectonics is dominated by southward thrusting on a major sole fault dipping north at approximately 6 within hercynian basement northerly directed thrusts of the north pyrenean zone and northern folded foreland are backthrusts from this sole fault a total orogenic shortening of 106 km in the central pyrenees was achieved between the palaeocene and oligocene at a time averaged rate of 0 62 cm yr 1 a thin skinned model requires that the north pyrenean fault is truncated by both northward and southward moving thrusts and occurs in the footwall of the sole fault some 60km north of its present surface trace

the structure evolution and symmetry of the magma poor rifted margins of the north and central atlantic a synthesis abstract magma poor rifted margins consistently show extreme crustal thinning accompanied by normal faulting the serpentinization of the mantle beneath crust thinned to less than 8 2 km and the unroofing of a broad zone of mantle within the continent ocean transition accompanied by the development of detachment and other large offset faults these observations are the logical result of the progressive extension of cool lithosphere away from thermal anomalies such as plumes although the paucity of magmatism may be explained by depth dependent extension of the lithosphere and by pre depleted sub crustal lithosphere rifting above initially cool sub lithospheric mantle also may explain the subsidence deficit observed at some margins synrift subsidence is buffered by the simultaneous influx of warmer oceanic asthenosphere as it extends thins and cools ductile creeping layers in the mid and deep crust become progressively more brittle resulting in increased coupling between the upper and lower crust and eventually the embrittlement of the entire crust faults cutting from the surface across the moho bringing water into the mantle and causing its serpentinization increased coupling and the development of serpentine detachments predict the development of late stage asymmetry once the entire crust is brittle such detachments are imaged on some margins and inferred on others analysis of the crustal structure across conjugate margins shows that these are approximately symmetric until this late stage when they become markedly asymmetric similar analyses show that depth dependent stretching of the crust is insufficient to explain the discrepancy between the amount of the visible extension along faults and the amount of crustal thinning instead this extension discrepancy may be related to the complex evolution of brittle deformation through multiple phases and styles of faulting related to the changes in the rheological character and strength of the lithosphere as it is thinned complex polyphase faulting continues after complete crustal separation resulting in the exhumation of broad expanses of peridotitic basement the top of which is everywhere marked by an exhumed slip surface similar to the corrugated surface observed at mid ocean ridges the similarity in processes between mantle unroofing and seafloor spreading makes the distinction between the cot and true oceanic crust difficult and possibly moot

search for the mantle nitrogen in the ultramafic xenoliths from san carlos arizona abstract mineral separates olivine ol clinopyroxene cp and orthopyroxene op of ultramafic xenoliths from san carlos have been analyzed for nitrogen and noble gases in an effort to evaluate the isotopic signatures for the sub continental mantle the concentrations of noble gases are generally small but in one clinopyroxene separate cp1 they are about an order of magnitude higher the gases seem mostly to be sited in fluid inclusions elevated isotopic ratios of 20 ne 22 ne 40 ar 36 ar 129 134 136 xe 132 xe with respect to air clearly show the presence of mantle noble gas components in san carlos xenoliths isotopic ratios of xe and ar show that the noble gas systematics in san carlos xenoliths can be explained as a mixture of morb and air like components nitrogen contents in these separates range from 0 1 to 1 5 ppm the 15 n varying from 2 to 5 in totals and from 9 to 10 in the temperature fractions the nitrogen data can be explained by the presence of at least three components a a light nitrogen component 15 n 9 of mantle origin b a heavy nitrogen component 15 n 15 from recycled materials and c an air like nitrogen component 15 n 0 which is incorporated during the emplacement of the host magma while the noble gas isotopic ratios cannot clearly distinguish between an atmospheric and a recycled component 15 n clearly resolves these two using the noble gas and nitrogen isotopic systematics and the end member values from the literature a contribution of 30 to 60 recycled nitrogen component has been estimated in the mantle source region of san carlos xenoliths

three dimensional gravity and magnetic modeling of crustal indentation and wedging in the western pyrenees cantabrian mountains 1 the complex crustal structure of the boundary zone between the iberian and european plates from the western pyrenees to the cantabrian mountains is probed by three dimensional 3 d gravity and magnetic modeling constrained by deep seismic profiles the 3 d modeling results support the presence of a continuous iberian crustal root and suggest that the geometry of the orogenic belt that formed in latest cretaceous tertiary times along the northern margin of iberia was conditioned by oblique structures separating areas characterized by different tectonic styles in the western pyrenees and the basque cantabrian basin a thick mesozoic basin presently incorporated to the pyrenean cantabrian belt the relatively narrow thinning of the crust inherited from the mesozoic rifting stage conditioned a structural style in which portions of the southward indenting european lower crust are interpreted to be back thrusted toward the north and uplifted to shallow depths promoting the appearance of significant potential field anomalies in the basque cantabrian basin the strongest aeromagnetic anomaly of the whole iberian mainland is superimposed on the eastern part of a well defined positive gravity anomaly similar in amplitude and wavelength to those located along the north pyrenean zone these observations suggest that the eastern part of the dense lower crustal causative body is strongly magnetized and may correspond to a gabbroic cumulate originated in the axis of the ancient mesozoic rift to the west tertiary compression affected the north iberian cantabrian passive continental margin whose geometry and inherited structures conditioned the formation of a double crustal delamination and the uplift of the cantabrian mountains

giant quartz vein systems in accretionary orogenic belts the evidence for a metamorphic fluid origin from δ 15 n and δ 13 c studies abstract nitrogen isotope compositions of hydrothermal micas in giant structurally hosted quartz vein systems place constraints on the origin of the hydrothermal fluids the vein systems are from neoarchean terranes in the superior province of canada and the norseman terrane western australia the four quartz vein systems studied in different terranes formed at metamorphic grades ranging from lower greenschist to lower amphibolite facies coevally with metamorphism of the host terrane nitrogen resides predominantly as nh 4 in hydrothermal mica for lower to upper greenschist facies quartz veins n contents and 15 n values of micas are between 40 and 200 ppm and 15 and 21 respectively whereas in quartz veins formed at the greenschist to amphibolite transition and lower amphibolite facies micas have n contents of 20 70 ppm and 15 n of 11 24 in contrast micas and k feldspars from granitoids in the neoarchean abitibi and red lake greenstone belts are characterized by systematically lower 15 n of 5 to 5 and generally lower n contents of 20 50 ppm comparable to other granitoids carbon and oxygen isotope compositions of hydrothermal ferroan dolomite and calcite show systematic depletions with increasing metamorphic grade the mean values range from 2 2 to 3 7 for 13 c and 13 8 to 12 3 for 18 o in veins formed at lower to upper greenschist facies but from 5 8 to 7 1 for 13 c and 11 4 to 9 8 for 18 o at higher metamorphic grades nitrogen isotope compositions rule out mantle 15 n mean 5 magmatic 15 n 5 to 15 n mean 4 4 2 0 for the quartz veins accordingly the results are consistent with fluids derived from metamorphic dehydration of oceanic crust and sediments within accretionary orogenic belts

nitrogen isotopic compositions and concentrations in marid xenoliths abstract nitrogen isotopic compositions and concentrations in micas from kimberlite hosted marid mica amphibole rutile ilmenite diopside suite of xenoliths from the kimberley area of the kaapvaal craton south africa were measured using continuous flow isotope ratio mass spectrometry and fourier transform infrared spectroscopy fourier transform infrared spectroscopy data suggest that the nitrogen in marid phlogopite is from ammonium in the mica structure the replacement of potassium by ammonium is the major mechanism for the storage of nitrogen within these phlogopites the 15n values of micas from marid xenoliths range from 11 to 9 and nitrogen contents range between 113 and 272 ppm the 15n enrichment of most samples relative to the average upper mantle 15n value of 5 suggests that the nitrogen reflects a recycled reservoir from subducted material within their source region the presence of nitrogen from a recycled reservoir indicates that sedimentary organic nitrogen in the sub continental lithosphere is not effectively cycled to the surface resulting in a geochemically heterogeneous upper mantle

the timing of marid metasomatism in the kaapvaal mantle an ion probe study of zircons from marid xenoliths abstract the precise timing of metasomatic events in the kaapvaal craton lithospheric mantle is poorly constrained and therefore it has proven difficult to relate mantle metasomatism in the source to igneous activity at the surface a suite of mica amphibole rutile ilmenite diopside bearing xenoliths marid represents the product of such metasomatic fluids or melts in this paper we report results of a shrimp and cathodoluminescence study on zircons from four marid samples from the kimberley cluster of pipes textures combined with experimental evidence suggest that zircons are late crystallizing phases in marids that form close to the solidus where the major precipitating phases are phlogopite and k richterite cathodoluminescence patterns reveal a complex growth history of the zircons involving strong deformation repeated events of crystallization resorption and or modification of the zircon composition possibly over several millions of years many of the u pb ages are significantly older than the intrusion age of the group i kimberlites of the kimberley cluster zircon ages in a marid xenolith from the wesselton kimberlite vary in the range 113 3 ma to 142 3 ma compared with a pipe age of 84 3 ma in two samples from the de beers bultfontein or dutoitspan pipes ages range from 85 5 to 119 2 ma in one and 80 4 to 90 2 ma in the other the ages obtained for the latter are indistinguishable from the pipe age of kimberlites belonging to the younger group i kimberlite event ca 80 95 ma zircons in this sample as well as the younger ages in the other may reflect real ages but most likely have lost radiogenic pb as a result of deformation and fluid or melt interaction the presence of pre group i ages in two of the samples demonstrates unambiguously that the metasomatism that yielded the older crystallization ages cannot be related to the group i kimberlite event instead minimum ages for the marid zircons coincide with the period of group ii kimberlite magmatism in the central to southeastern kaapvaal craton this coincidence in ages would be consistent with the contention based on experimental evidence that marid type rocks can be derived from group ii precursor magmas by olivine fractionation and exsolution of a carbonatitic component an alternative possibility not excluded by the zircon minimum ages is a genetic relation between marid metasomatism and karoo magmatism

oxygen and hydrogen isotopic composition of phlogopites and amphiboles in diamond bearing kimberlite hosted marid xenoliths constraints on fluid rock interaction and recycled crustal material in the deep continental lithospheric mantle abstract marid mica amphibole rutile ilmenite diopside xenoliths are transported from the deep cratonic lithosphere to the earth s surface by cretaceous kimberlites emplaced in the kimberley area of the kaapvaal craton marid xenoliths have high modal abundances 70 80 vol of mica and amphibole indicating their origin from a hydrous source the 18o values 4 7 18o 6 9 of phlogopite micas from 14 marid samples indicate that these minerals are both 18o enriched and 18o depleted with respect to the average upper mantle 18o value of 5 8 0 6 the range of 2h values of phlogopites 83 2h 53 n 14 of marid xenoliths are slightly larger than the average mantle 2h value 70 10 the oxygen 18ophlogopites amphibole 0 4 and 0 4 and hydrogen 2hphlogopite amphibole 14 and 36 isotopic disequilibrium recorded from two marid xenoliths suggests the duration of the last isotopic exchange possibly just before the kimberlite emplacement between these minerals and metasomatic fluids was too short to reach isotopic equilibrium our model calculation indicates that the phlogopites of marid xenoliths underwent isotopic exchange with fluids of 18o 5 5 to 10 2h 62 to 90 the range of 18o value of the calculated metasomatic fluids resembles the oxygen isotopic composition of the primary mantle carbonate 6 9 suggesting interaction between carbonatic melt and marid xenoliths in the continental lithospheric mantle furthermore 18o values of phlogopites together with previously published nitrogen isotope data 11 15n 9 banerjee et al 2015 indicates incorporation of inhomogeneously distributed recycled crustal material from subducted crust within their source magma therefore o h n isotope data for marid xenoliths indicates their crystallization from geochemically heterogeneous magma in the upper continental mantle and subsequent metasomatism with mantle fluids

storage and mobility of nitrogen in the continental crust evidence from partially melted metasedimentary rocks mt stafford australia abstract the mt stafford region central australia provides well exposed metasedimentary rocks whose protoliths were deposited at ca 1 84 1 81 ga and that were metamorphosed at greenschist to granulite facies pressure temperature conditions at 1 8 ga the higher grade rocks show evidence of low pressure partial melting 2 4 kbars over a temperature range of 650 to 850 c these exposures afford evaluation of the extent to which n is retained through devolatilization and partial melting reactions experienced in the shallow to mid continental crust in the mt stafford metapelitic metapsammitic suite whole rock 15 n air values of the lowest grade greenschist facies rocks zone 1 range from 2 3 to 6 2 mean 3 6 1 1 5 n 7 and values for the highest grade granulite facies rocks zone 4 range from 2 1 to 8 5 mean 5 2 1 2 1 n 20 six of the twenty samples at the highest grade have values higher than those of the greenschist rocks regarded as likely protoliths all but a few of the zone 4 rocks have n concentrations lower than the mean n concentration for the lowest grade rocks ranges of 107 346 ppm mean 254 ppm for zone 1 rocks and 43 361 ppm mean 185 ppm for zone 4 rocks for the higher grade rocks which experienced multiple partial melting reactions varying retention of n as nh 4 in k feldspar or as n 2 in cordierite may indicate that n is held in peritectic products of partial melting rather than in the melt although assessments of element loss in the mt stafford suite are greatly complicated by the large degree of protolith related heterogeneity some elements do show modest decline in concentration with increasing grade consistent with their loss during devolatilization and partial melting nitrogen appears most similar in behavior to rb the lile most similar in ionic radius to nh 4 but of these two elements n shows somewhat greater evidence for whole rock loss k 2 o shows only very subtle hints of whole rock loss in some samples and cs shows considerably greater loss relative to n and rb resulting for example in increases in rb cs at the higher grades increased whole rock ba rb for some higher grade samples relative to that for lower grade equivalents likely reflects the formation of a major ba reservoir in k feldspar at the expense of biotite resulting in no obvious whole rock ba loss with rb liberated from biotite breakdown partitioning into the melts that at least partly left the system reduced whole rock b concentrations at the higher grades resulted from the breakdown of tourmaline during the melting reactions these varying degrees of reduction in whole rock n rb cs and b and possibly k 2 o concentration are accompanied by decreased concentrations in h 2 o as indicated by loi li and u the loss of u resulting in increased th u in the highest grade rocks apparent differential loss of these elements based on the whole rock data could reflect the amounts of melt produced and the extents to which the melts were removed at the scales sampled by the hand specimens that were analyzed six of the twenty zone 4 samples showing greater shift in 15 n to values of 7 4 to 8 4 tend to be among the samples showing the largest changes in other major and trace element concentrations and ratios believed to reflect melt removal e g k 2 o cs tio 2 b al 2 o 3 th u and ratios among rb sr ba and cs the metasedimentary rocks at mount stafford also contain 217 to 1186 ppm c likely as reduced c graphite but at the higher grades probably also as co 2 in the channels of cordierite at greenschist grade whole rock 13 c v pdb values are relatively uniform with organic compositions mean 25 1 1 1 6 n 7 but at the highest grade zone 4 values are as high as 17 7 mean 22 2 1 2 3 n 8 overall c and n apparently largely of organic origin show surprising retention in rocks having experienced peak temperatures of 800 c demonstrating their compatibility in mineral phases in fluid and melt residues for n as nh 4 in k feldspar and as n 2 in cordierite for c as graphite and as co 2 in cordierite these data have implications for deep earth n cycling bearing on the size of the n reservoir in the mid continental crust and thus long term storage of n previously residing in the atmosphere and biosphere and for the use of the 15 n of upper crustal intrusive rocks as a tracer of their deep crustal sources

three dimensional circulation in the nw africa coastal transition zone abstract high resolution data collected southeast of the canary islands during late winter 2006 are analyzed to describe the hydrography and three dimensional circulation in the coastal transition zone off nw africa the data are optimally interpolated over a regular grid the geostrophic velocity field is calculated and the q vector formulation of the omega equation is used to compute the quasi geostrophic qg mesoscale vertical velocity the coastal transition zone is divided into upwelling frontal and offshore regions with distinct physical and dynamic characteristics the upwelling region is characterized by cold and weakly stratified waters flowing towards the equator with a poleward undercurrent of approximately 0 05 m s 1 over the continental slope the frontal region exhibits a southwestward baroclinic jet associated with cross shore raising isopycnals the jet transport is close to 1 sv with maximum velocities of 0 18 m s 1 at surface decreasing to 0 05 m s 1 at 300 db vertical sections across the frontal region show the presence of deep eddies probably generated by the topographic blocking of the islands to the southward current as well as much shallower eddies that likely have arisen as instabilities of the baroclinic upwelling jet the qg mesoscale vertical velocity field is patchy estimated to range from 18 to 12 m day 1 with the largest absolute values corresponding to an anticyclonic eddy located south of fuerteventura island these values are significantly larger than estimates for other vertical velocities diapycnal vertical velocities associated with mixing in the frontal region a few meters per day and wind induced vertical velocities non linear ekman pumping arising from the interaction between the wind stress and the background vorticity maximum values of a few meters per day linear ekman pumping due to the divergence of ekman transport a fraction of a meter per day or the coastal constraint in the upwelling region about 0 7 m day 1 however the patchiness in both the qg mesoscale vertical velocity and the non linear ekman pumping velocity cause their integrated vertical transports to be one order of magnitude smaller than either coastal ekman transport 0 08 sv integrated linear ekman pumping 0 05 sv or diapycnal transfer about 0 1 0 2 sv the pattern of the near surface fluorescence field is a good indicator of these different contributions with large homogeneous values in the coastal upwelling region and a patchy structure associated with the offshore mesoscale structures

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

re assessing the nitrogen signal in continental margin sediments new insights from the high northern latitudes organic and inorganic nitrogen and their isotopic signatures were studied in continental margin sediments off spitsbergen we present evidence that land derived inorganic nitrogen strongly dilutes the particulate organic signal in coastal and fjord settings and accounts for up to 70 of the total nitrogen content spatial heterogeneity in inorganic nitrogen along the coast is less likely to be influenced by clay mineral assemblages or various substrates than by the supply of terrestrial organic matter tom within eroded soil material into selected fjords and onto the shelf the 15 n signal of the inorganic nitrogen 15 ninorg in sediments off spitsbergen seems to be appropriate to trace tom supply from various climate and ecosystem zones and elucidates the dominant transport media of terrigenous sediments to the marine realm moreover we postulate that with the study of sedimentary 15 ninorg in the atlantic arctic gateway climatically induced changes in catchment s vegetations in high northern latitudes may be reconstructed the 15 norg signal is primarily controlled by the availability of nitrate in the dominating ocean current systems and the corresponding degree of utilization of the nitrate pool in the euphotic zone not only does this new approach allow for a detailed view into the nitrogen cycle for settings with purely primary produced organic matter supply it also provides new insights into both the deposition of marine and terrestrial nitrogen and its ecosystem response to paleo climate changes

nitrogen isotope systematics of mesothermal lode gold deposits metamorphic granitic meteoric water or mantle origin archean gold bearing quartz vein systems constitute one of the most important classes of precious metal deposits however their origin remains controversial mantle granitoid meteoric water and metamorphic related models do not resolve this controversy new n and nitrogen isotope data on hydrothermal muscovite from six gold camps from the late archean superior province of canada and biotite from nine au mineralized locations from the norseman wiluna greenstone belt western australia are reported the majority of muscovites and biotites have n contents of 20 190 ppm and 15 n of 10 20 and 10 70 ppm and 10 24 respectively the 15 n of the mantle is 5 and of granitoids is 0 10 both with generally low n contents organic n is 0 10 meteoric water is 1 9 9 4 and metamorphic rocks are 3 18 increasing with higher grade accordingly the data appear to rule out a mantle hypothesis granitoid related magmatic processes or meteoric water for the deposits but are consistent with ore fluids derived by metamorphic dehydration reactions

deep structure of the armorican basin bay of biscay a review of norgasis seismic reflection and refraction data the bay of biscay is bounded to the north by the north biscay margin which comprises the western approaches and armorican segments in the 1970s and 1980s most researchers considered this margin typical of a non volcanic passive margin it is characterized by a striking succession of tilted blocks beneath which occurs the s reflector and the continent ocean boundary is abrupt this paper examines the armorican segment and is based on a study of all early seismic profiles together with new multichannel reflection and refraction seismic data norgasis cruise an important result is the discovery of a 80 km wide ocean continent transition zone that coincides with the armorican basin a deep sedimentary basin it is characterized by a high velocity lower crustal layer 7 4 7 5 km s 1 overlain by sediments the other results are 1 the main crustal thinning occurs exclusively under the narrow continental slope 2 the tilted blocks and the s reflector are observed only at the base of the continental slope in the narrow domain called the neck area 3 the north biscay ridge is a large oceanic plateau present only off the nw armorican margin rather than a long ridge elongated off the whole north biscay margin

hydrogen isotope systematics of submarine basalts the d h ratios and water contents in fresh submarine basalts from the mid atlantic ridge the east pacific rise and hawaii indicate that the primary d h ratios of many submarine lavas have been altered by processes including 1 outgassing 2 addition of seawater at magmatic temperature and 3 low temperature hydration of glass decreases in d and h2o from exteriors to interiors of pillows are explained by outgassing of water whereas inverse relations between d and h2o in basalts from the galapagos rise and the famous area are attributed to outgassing of ch4 and h2 a good correlation between d values and h2o is observed in a suite of submarine tholeiites dredged from the kilauea east rift zone where seawater added directly to the magma affected only the isotopic compositions of hydrogen and argon analyses of some glassy rims indicate that the outer millimeter of the glass can undergo lowtemperature hydration by hydroxyl groups having d values as low as 100 d values vary with h2o contents of subaerial transitional basalts from molokai hawaii and subaerial alkali basalts from the society islands indicating that the primary d values were similar to those of submarine lavas extrapolations to possible unaltered d values and h2o contents indicate that the primary d values of most thoteiite and alkali basalts are near 80 5 the weight percentages of water are variable 0 15 0 35 for mor tholeiites about 0 25 for hawaiian tholeiites and up to 1 1 for alkali basalts the primary d values of 80 for most basalts are comparable to those measured for deep seated phlogopites these results indicate that hydrogen in marked contrast to other elements such as sr nd pb and o has a uniform isotopic composition in the mantle this uniformity is best explained by the presence of a homogeneous reservoir of hydrogen that has existed in the mantle since the very early history of the earth

western extension of the iberian european plate boundary during the early cenozoic pyrenean convergence a new model abstract a dense seismic net work allows of drawing the western prolongation of the northern boundary of the iberian plate this early cenozoic deformed boundary is disrupted by two prominent nw se transform faults a kinematic reconstruction with a nw late cretaceous lower eocene motion of the iberian plate is proposed the azores biscay rise is interpreted as a short lived subduction zone whereas king s trough could be a transform fault

initiation of an active margin at the north iberian continent ocean transition 1 the north iberian or cantabrian margin located at the southern flank of the bay of biscay underwent successive tectonic regimes of rifting passive margin and compression from mesozoic to tertiary times a complete crustal cross section of the north iberian margin from the abyssal plain to the shoreline and a reconstruction of its undeformed upper cretaceous structure are presented here it is constrained after the compilation and interpretation of different geophysical data sets recently available in the area the reflective pattern is provided by deep seismic reflection profile escin 4 complemented by commercial profiles and well information from the north iberian platform and the velocity depth control comes from an onshore offshore wide angle seismic profile tested also with gravity modeling the detailed cross section of the meso tertiary basins that fill the platform and abyssal plain shows structures from the three main tectonic events 1 normal faults and asymmetric basins from the permian to lower cretaceous extensional stage 2 upper cretaceous sediments deposited under stable conditions during the passive margin period and 3 inverted faults thrusts and folds related to the tertiary compression the deep structure of the crust beneath the margin is poorly constrained from escin 4 profile that shows reflectivity in the lower crust only at a small area under the platform however the corresponding wide angle experiment provides a conspicuous image of the moho that shows a continued deepening toward the continent on the basis of the geophysical results we propose a new model for this margin where the lower crust is detached and underthrusted to the south as a result of the partial closure of the bay of biscay an interpreted mesozoic crustal scale extensional detachment could be the weakness zone that allowed the lower crust to slide southward under the upper crust resulting in the indentation of the cantabrian margin lower crust into the iberian crust plate convergence stopped at an early stage making this a unique area to study the initial stages of deformation of a passive margin

c and n isotopic composition and the infrared absorption spectra of coated diamonds evidence for the regional uniformity of co2h2o rich fluids in lithospheric mantle abstract the 13 c and 15 n values nitrogen abundances and nitrogen aggregation states of coated diamonds from botswana angola sierra leone and siberia have been determined a single cubic micro diamond from the northern territory australia was also analysed the cubic coats of the diamonds and the cubic diamond from australia had a restricted range in isotope composition 13 c 7 2 to 4 1 15 n 8 7 to 1 7 in contrast the cores of the coated diamonds were found to be highly variable 13 c 21 1 to 1 9 and 15 n 2 8 to 12 1 with the majority being positive all of the coats gave the type iaa absorption spectra together with others due to micro inclusions dominated by h 2 o and co 2 whereas the cores contained nitrogen that was more highly aggregated the results suggest that coated diamonds were formed following the influx of co 2 h 2 o rich fluids into diamond bearing lithosphere pre existing diamonds acted as seeds for renewed growth and these are now the cores of the diamonds these cores may be very variable in terms of morphology isotopic composition age nitrogen aggregation state and crystallinity depending on the particular history of the source regions and the conditions of diamond growth it is believed that the influx of volatiles and the growth of the coats was linked to kimberlite magmatism the 13 c and 15 n results for the coats indicate that in terms of c and n isotope composition the source of co 2 h 2 o rich fluids is globally quite homogeneous it is probably located beneath continental lithosphere and in addition may have characteristics similar to the source of the ocean island basalts

isotopic variations of the fixed nitrogen in metamorphic rocks the content and isotopic composition of fixed nitrogen nh 4 n in metasedimentary rocks phyllites mica schists and gneisses from prograde metamorphic zones in the erzgebirge saxon ore mountains g d r were measured and show that the nitrogen content decreases and 15n increases with increasing metamorphic grade the geochemical and isotopic behaviour of nitrogen during contact metamorphism was investigated in a mica schist profile through the contact aureole of a granitic pluton the nitrogen concentrations of the wall rocks decrease towards the contact whereas the 15n values become higher various model experiments were carried out in the laboratory to explain the changes observed in the rock samples the nitrogen isotope fractionation factor was determined for the isotopic exchange in the system ammonium sulphate ammonia at 250 c 1 0143 0 0012 and 350 c 1 0128 0 0006 in accordance with the model experiments the conclusion seems warranted that the change in nitrogen content and its isotopic composition in rocks during metamorphic processes depend mainly on the metamorphic temperature

structure of the nankai trough accretionary zone from multichannel seismic reflection data new multichannel seismic reflection data collected over the nankai trough image the accretionary complex in two areas the international program of ocean drilling leg 87 transect area western area and the region of upcoming ocean drilling program leg 131 eastern area the incoming shikoku basin sedimentary section consists of hemipelagic clays and thin terrigenous turbidites the basin section is overlain by a trench wedge that is 12 16 km wide and 350 750 m thick at the thrust front accretionary deformation begins in a protothrust zone that is characterized by thickening and seaward tilting of the trench wedge the zone in the western area is 4 5 km wide and is characterized by kink folds the zone in the eastern area is only 2 5 km wide and does not exhibit such folds the frontal thrusts in each area are imaged as fault plane reflections and ramp upward from within the basin hemipelagic section the overthrusting sediments form fault bend folds over these ramps thrust spacing at the toe of the slope is 1 5 2 5 km the second thrust cuts up from an inferred decollement within the shikoku basin sedimentary section in the eastern area a reflection marking the top of the basin pelagic sediment section changes from normal to reversed polarity about 6 3 km seaward of the thrust front and underlies the entire protothrust zone this reflector continues with reversed polarity under the accretionary complex and is at the level of the basal decollement the underlying basin pelagic section is apparently thrust undisturbed beneath the accretionary prism the reversal of polarity indicates a change in reflection coefficient that is due to a combination of decreasing seismic velocity and density across the interface this decrease in velocity and density may indicate that the decollement is a zone of high porosity due to fluid expulsion from deeper within the accretionary prism the reflections from the first and second thrusts are also reversed polarity possibly indicating that they also are pathways of fluid expulsion the critical wedge taper of the western area is greater than that of the eastern area an observation that is consistent with the existence of an overpressured decollement in the eastern area

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

precambrian ammonium biogeochemistry a study of the moine metasediments scotland abstract the content and isotopic composition of ammoniacal nitrogen have been determined in a suite of amphibolite facies metasediments of precambrian age whole rock samples and mica separates from the moine succession proterozoic of scotland were analysed by a combination of capacitance manometry and static vacuum mass spectrometry prior to the analyses the presence of the ammonium ion was confirmed by obtaining infrared ir absorption spectra from the micas principally biotites whole rock ammonium contents are high for amphibolite facies metasediments 140 422 ppm the ammonium ion was not detected in the ir absorption spectra of biotites from one schist however this sample contains neither garnet nor white mica for most of the samples the 15n values are very positive between 12 4 and 16 6 with one sample having a lower value of 8 4 the major variations between samples can be interpreted in terms of original sedimentary features for the ammonium bearing samples muscovites have concentrations between 365 and 633 ppm biotites between 845 and 1739 ppm for individual samples nh4 mu nh4 bi varies between 0 31 and 0 43 a much narrower range than has been reported previously there are no significant or consistent differences in 15n between co existing biotite and white mica nor between the 15n values of the mineral separates and their respective whole rock values the latter suggests minimal selective partitioning of isotopes between micas and plagioclase feldspar the only other potential host for ammonium in the rocks assuming that the ammonium has been derived from organic matter originally present at the time of deposition and by comparison with previous studies it can be inferred that the original 15n value of the moine sediments was somewhere between 5 and 10 similar to recent sediments this suggests that the nitrogen cycle in the proterozoic shelf sea from which the moine sediments were deposited was broadly similar to the present day overall the study underlines how under developed the n system is compared to other stable isotope systems notably c and s and we use the opportunity to highlight some areas that could be developed in the future however one aspect is clear future ammonium studies of metamorphic rocks will need to be performed at high resolution visible scale of heterogeneity with strong mineralogical petrological and field controls

multiple growth events during diamond genesis an integrated study of carbon and nitrogen isotopes and nitrogen aggregation state in coated stones the internal structure and growth history of diamonds have been investigated by the study of carbon isotopes and the abundance isotope composition and aggregation state of nitrogen polished plates of zoned diamonds coated stones were laser sectioned for infrared mapping and isotope profiling nine small cubic and three small octahedral diamonds from zaire and two coated stones and five small cubic diamonds specifically from the mbuji mayi area of that country were also investigated the isotope composition and infrared characteristics of the diamonds of cubic habit including coats were found to be indistinguishable with 13c in the range 5 9 to 7 5 and all the nitrogen being present as the paired structure iaa with a 15n of between 3 1 and 8 0 the diamonds of octahedral habit including the cores of the coated stones were more variable 13c varied from 4 9 to 9 8 infrared spectra of the octahedral diamond exhibited either strong iaa characteristics or a combination of iaa and iab platelets were present in most cases 15n values from octahedral diamonds varied from 5 8 to 13 4 the data suggest that the octahedral diamonds represent a variety of growth events separated in time and or space and that the diamonds resided in the lithosphere for a period sufficient for thermal maturation in the case of the coated stones the octahedral diamonds were later involved in an event which added a component from a single relatively homogeneous reservoir cubic habit diamonds were formed at the same time this latter event is believed to be related to the kimberlite eruption comparison of the data with carbon isotope analyses of cubic diamond from other sources suggests that this reservoir could be widespread

the marconi reflection seismic data a view into the eastern part of the bay of biscay abstract seismic data acquisition for the marconi project took place in 2003 in the eastern half of the bay of biscay the overall goal of the multichannel experiment was to collect seismic data to elucidate the structure and evolution of the southern margin of the bay where an along the margin transition between oceanic subduction in the west and continental convergence in the east occurs and its relationship to the pyrenean realm we describe the multichannel experiment and present an interpretation of the abyssal plain sector of the profiles altogether eleven regional seismic reflection profiles were collected with a total length of 1800 km between the longitudes 6 and 2 w and latitudes 43 5 and 46 n the seismic profiles show first images of the thick sedimentary pile that covers the eastern abyssal plain of the bay the interpretation includes three sedimentary sequences separated by unconformities that correspond to the pre syn and post alpine sequences the post orogenic deposits lay unconformably over the previous compressional structures in the eastern part of the bay floored by transitional crust these compressional features are evident in the presence of a young accretionary prism sealed at its first stages of development the overall structure and shape is similar to those of active subduction prisms worldwide but evidencing differences in width and sediment wedge thickness from west to east along the margin buoyancy of the transitional crust and resistance to subduction led to stronger plate coupling towards the east where oceanic crust is absent and may be the main cause for these morphological changes along the east west traverse of the wedge the marconi multichannel deep seismic dataset provides the first estimation of the thickness of the sediment load on the 5000 m deep abyssal plain of bay of biscay where no direct data were available

nitrogen isotope compositions of metasedimentary rocks in the catalina schist california implications for metamorphic devolatilization history abstract in the catalina schist subduction zone metamorphic complex california metasedimentary rocks show a decrease in n concentration and an increase in 15nair with increasing metamorphic grade lowest grade lawsonite albite rocks contain 632 185 ppm n with 15 n 1 9 0 6 whereas highgrade amphibolite equivalents contain 138 76 ppm n with 15 n 4 3 0 8 loss of n accompanied devolatilization reactions that evolved h2o rich c o h s n fluids through consumption of chlorite and phengitic white mica and production of mineral assemblages containing muscovite biotite garnet and kyanite whole rock n concentrations of up to 200 ppm in veins and pegmatites produced during high p t metamorphism reflect the redistribution of n during devolatilization and partial melting of the metasedimentary rocks bulk fluid rock n isotope fractionations 15n 15nfluid 15nrock of 1 5 1 were calculated with the rayleigh distillation equation taking into account variability in rock composition by comparison of samples with similar k2o concentrations these fractionations are similar to but slightly lower than published calculated fractionations for n2 nh4 exchange at the temperature range of 350 600 c over which most of the devolatilization occurred in the catalina schist approximately 3 4 to 2 25 the n systematics appear to be explained by n2 nh4 exchange and a devolatilization process intermediate in behavior to batch volatilization and rayleigh distillation the observed shifts in n concentration and 15n cannot be explained by nh3 nh4 exchange at these temperatures using the equilibrium models the distillation devolatilization process implicated in this study may govern the behavior of other trace elements partitioned into hydrous fluids during devolatilization e g b cs u similarity of the calculated fluid 15n 1 5 to 5 5 with compositions of natural gases inferred to be derived from metasedimentary sources indicates the possibility of using n as a tracer of large scale volatile transport

nitrogen rich fluid in the upper mantle fluid inclusions in spinel dunite from lanzarote canary islands fluid inclusions ranging from pure n2 to pure co2 occur in olivine porphyroclasts in spinel dunite xenoliths chrome diopside suite from two localities within the quaternary to historic alkaline lavas of lanzarote canary islands this is the first report of fluid inclusions containing major amounts of n2 in mantle xenoliths the nitrogen rich fluid inclusions predate at least one generation of nitrogen free carbon dioxide inclusions textural evidence indicates that the inclusions were trapped within the upper mantle some of the nitrogen rich fluid inclusions are intimately associated with solid inclusions of spinel the nitrogen rich fluid was most likely produced in situ by oxidation dehydration reactions destabilizing ammonium bearing silicate minerals phlogopite amphibole increasing oxygen fugacity or possibly increasing temperature of the mantle this process could be related to an event of co2 and silicate melt injection at 6 8 kbar neumann et al in press or to some earlier event in the evolution of the mantle beneath lanzarote the existence of a n2 rich fluid phase in at least some mantle lithology ies at certain conditions is demonstrated by these data this discovery has consequences for the understanding of the evolution of the mantle below the canary islands as well as for the global nitrogen budget

crustal structure and orogenic material budget in the west central pyrenees surface and subsurface data are combined to construct a crustal scale cross section of the western central pyrenees france and spain at the boundary between the european and iberian plates the position of moho reflections in the ecors arzacq reflection profile suggests a tectonic wedge of european crust and upper mantle had indented the iberian plate at lower crustal levels the european wedge is overlain by an upper iberian wedge thus constituting a double stacked wedge geometry the upper wedge was delaminated and deformed giving rise to the pyrenean orogenic prism manifested as a bivergent fan in upper crustal levels the underthrust lower iberian plate has been imaged to depths of 55 60 km but crustal budget considerations based on a palinspastic reconstruction require that this continental root subducted to depths up to 90 km total orogenic contraction calculated from surface structures is about 75 80 km which was accomplished between the latest cretaceous and the early miocene at an averaged rate of 1 2 mm yr consistent with these moderate values exhumation of the orogen is much less than in the more shortened eastern parts of the range paleozoic basement and preorogenic mesozoic rocks are little eroded and much of the exhumation involved cannibalization of early foreland basins which once covered the entire poorly emergent orogen at this transect this resulted in a continuous process of sediment recycling and coupled with a considerable lateral arrival of material a bulk negative erosion sedimentation budget