incorporating self consistently calculated mineral physics into thermochemical mantle convection simulations in a 3 d spherical shell and its influence on seismic anomalies in earth s mantle 1 phase assemblages of mantle rocks calculated from the ratios of five oxides cao feo mgo al2o3 sio2 by free energy minimization were used to calculate the material properties density thermal expansivity specific heat capacity and seismic velocity as a function of temperature pressure and composition which were incorporated into a numerical thermochemical mantle convection model in a 3 d spherical shell the advantage of using such an approach is that thermodynamic parameters are included implicitly and self consistently obviating the need for ad hoc parameterizations of phase transitions which can be complex in regions such as the transition zone particularly if compositional variations are taken into account convective planforms for isochemical and thermochemical cases are however not much different from those computed using our previous simple parameterized reference state which means that our previous results are robust in this respect the spectrum and amplitude of seismic velocity anomalies obtained using the self consistently calculated material properties are more realistic than those obtained when seismic velocity is linearly dependent on temperature and composition because elastic properties are dependent on phase relationship of mantle minerals in other words pressure and temperature in all cases the spectra are dominated by long wavelengths spherical harmonic degree 1 to 2 similar or even longer wavelength than seismic tomographic models of earth which is probably due to self consistent plate tectonics and depth dependent viscosity in conclusion this combined approach of mantle convection and self consistently calculated mineral physics is a powerful and useful technique for predicting thermal chemical phase structures in earth s mantle however because of uncertainties in various parameters there are still some shortcomings in the treatment of the postperovskite phase transition additionally transport properties such as thermal conductivity and viscosity are not calculated by this treatment and are thus subject to the usual uncertainties

first petrographic results on impactites from the yaxcopoil 1 borehole chicxulub structure mexico the icdp yaxcopoil 1 yax 1 borehole located 60 km south southwest of the center of the chicxulub impact structure intercepted an interval of allogenic impactites depth of 795 895 m petrographic analysis of these impactites allows them to be differentiated into five units based on their textural and modal variations unit 1 795 922 m comprises an apparently reworked poorly sorted and graded fine grained clast supported melt fragment bearing suevitic breccia the interstitial material similar to units 2 and 3 is permeated by numerous carbonate veinlets units 2 823 846 m and 3 846 861 m are groundmass supported breccias that comprise green to variegated angular and fluidal melt particles the groundmass of units 2 and 3 comprises predominantly fine grained calcite altered alkali element ca and si rich cement as well as occasional lithic fragments unit 4 861 885 m represents a massive variably devitrified and brecciated impact melt rock the lowermost unit unit 5 885 895 m comprises highly variable proportions of melt rock particles mrp and lithic fragments in a fine grained carbonate dominated groundmass this groundmass could represent either a secondary ydrothermal phase or a carbonate melt phase or both units 1 and 5 contain well preserved foraminifera fossils and a significantly higher proportion of carbonate clasts than the other units all units show diagnostic shock deformation features in quartz and feldspar clasts our observations reveal that most felsic and all mafic mrp are altered they register extensive k metasomatism in terms of emplacement we suggest that units 1 to 3 represent fallout suevite from a collapsing impact plume whereby unit 1 was subsequently reworked by resurging water unit 4 represents a coherent impact melt body the formation of which involved a significant proportion of crystalline basement unit 5 is believed to represent an initial ejecta ground surge deposit

self consistent thermodynamic description of silicate liquids with application to shock melting of mgo periclase and mgsio3 perovskite summary we develop a self consistent thermodynamic description of silicate liquids applicable across the entire mantle pressure and temperature regime the description combines the finite strain free energy expansion with an account of the temperature dependence of liquid properties into a single fundamental relation while honouring the expected limiting behaviour at large volume and high temperature we find that the fundamental relation describes well previous experimental and theoretical results for liquid mgo mgsio3 m g2sio4 and sio2 we apply the description to calculate melting curves and hugoniots of solid and liquid mgo and mgsio3 for periclase we find a melting temperature at the core mantle boundary cmb of 7810 160 k with the solid hugoniot crossing the melting curve at 375 gpa 9580 k and the liquid hugoniot crossing at 470 gpa 9870 k for complete shock melting of periclase we predict a density increase of 0 14 g cm 3 and a sound speed decrease of 2 2 km s 1 for perovskite we find a melting temperature at the cmb of 5100 100 k with the perovskite section of the enstatite hugoniot crossing the melting curve at 150 gpa 5190 k and the liquid hugoniot crossing at 220 gpa 5520 k for complete shock melting of perovskite along the enstatite principal hugoniot we predict a density increase of 0 10 g cm 3 with a sound speed decrease of 2 6 km s 1

convective modifications of a geostrophic eddy field ocean convection often occurs in regions of mesoscale eddy activity where convective mixing and geostrophic eddy dynamics interact the authors examine the interactions between a group of geostrophic eddies and convective mixing induced by surface buoyancy loss through a series of numerical simulations using a nonhydrostatic boussinesq model the eddies are initially baroclinic with a surface intensified density anomaly and sheared flow but they are stable to baroclinic instability because of their small size in the absence of buoyancy loss eddy mergers occur much as in previous studies of geostrophic turbulence with the addition of surface buoyancy loss the surface stratification is eroded by small scale convection the convective mixing is highly heterogeneous being deeper in regions of weaker initial stratification and shallower in more strongly stratified regions the deformation radius is reduced in mixing regions and the weakly stratified eddies become baroclinically unstable the barotropic component of kinetic energy increases as convection proceeds largely due to the conversion of the available potential energy of the eddies in the baroclinic instability process the convective forcing therefore provides a means of increasing the barotropic component of the eddy kinetic energy by enabling the baroclinic instability the fluid is efficiently homogenized by the energetic eddy field leading to a few isolated eddies separated by a well mixed fluid these simulations provide a possible explanation for energetic eddy fields observed during convective periods in the labrador sea

melting curve of mg fe sio3 perovskite to 96 gpa evidence for a structural transition in lower mantle melts the melting temperature of mg fe sio3 perovskite the dominant mineral phase of the earth s lower mantle has been measured to a pressure of 96 10 gpa below 60 gpa we find good agreement with the previous measurement of heinz and jeanloz 1987a and above 60 gpa the melting curve of silicate perovskite has a small positive slope of 19 5 5 5 k gpa the melting point of mg0 9fe0 1 sio3 perovskite is 3800 300 k at 96 gpa by extrapolation to 136 gpa it is 4500 500 k at the core mantle boundary these values provide an upper limit to the geotherm through the solid mantle and they are compatible with recent estimates of the temperature in the core being high 4500 k at the core mantle boundary our melting curve implies that the volume change on melting increases at 60 gpa from vm 0 0 0 2 cm mole to vm 0 16 0 03 cm mole we derive an equation of state for the melt from our data and find that a highly coordinated structure is required to explain the molar volume of liquid mg fe sio3 at pressures above 20 gpa

numerical modelling of spontaneous slab breakoff dynamics during continental collision slab detachment or breakoff is directly associated with phenomena like morphological orogenesis occurrenceofearthquakesandmagmatism atdepththedetachmentprocessisslowand characterized by viscous rheolgy whereas closer to the surface the process is relatively fast and plastic using a 2d mantle model 1500 km deep and 4000 km wide we investigated with finite difference and marker in cell numerical techniques the impact of slab age convergence rate and phase transitions on the viscous mode of slab detachment in contrast to previous studies exploring simplifiedbreakoffmodelsinwhichtheblockageresponsibleforinducingbreakoffiskinematically prescribed we constructed a fully dynamic coupled petrological thermomechanical model of viscousslabbreakoff inthismodel forcedsubductionofa700 km longoceanicplatewasfollowed bycollisionoftwocontinentalplatesandspontaneousslabblockingresultingfromthebuoyancyof thecontinentalcrustonceithadbeensubductedtoadepthof100 124 km typically fivephasesof model development can be distinguished a oceanic slab subduction and bending b continental collision initiation followed by the spontaneous slab blocking thermal relaxation and unbending in experiments with old oceanic plates in this phase slab roll back occurs c slab stretching and necking d slab breakoff and accelerated sinking and e post breakoff relaxation our experiments confirm a correlation between slab age and the time of spontaneous viscous breakoff as previously identified in simplified breakoff models the results also demonstrate a non linear dependence of the duration of the breakoff event on slab age a positive correlation being characteristic of young 50 ma slabs while for older slabs the correlation is negative the increasing duration of the breakoff with slab age in young slabs is attributed to the slab thermal thickness which increases both the slab thermal relaxation time and duration of the neckingprocess inolderslabsthistendencyiscounteractedbynegativeslabbuoyancy whichgen eratehigherstressesthatfacilitateslabneckingandbreakoff apredictionfromourbreakoffmodels isthattheolivine wadsleyitetransitionplaysanimportantroleinlocalizingviscousslabbreakoffat depths of 410 510 km due to the buoyancy effects of the transition

sampling characteristics from isobaric floats in a convective eddy field during the recent labrador sea deep convection experiment numerous isobaric floats were deployed interpretation of the quasi lagrangian measurements from these floats requires an understanding of any biases that may be introduced by the response of the floats to the flow in which they are embedded to investigate the float measurement biases in convecting flow numerical simulations of isobaric floats in a domain containing several mesoscale eddies have been performed when a surface heat loss is applied spatially variable convective mixing and baroclinic instability result the authors find that without surface cooling probability density functions of eulerian and isobaric float measurements of tracers and velocities are very similar given an initial distribution of isobaric floats that is random with respect to the initial features of the tracer field however with cooling isobaric statistics are biased compared to the eulerian statistics in particular in near surface regions isobaric floats appear to oversample regions of dense downwelling fluid since in near surface layers downwelling dense fluid is associated with convergence a probable explanation of the isobaric float biases is a tendency for floats to concentrate in regions of horizontal convergence also with cooling floats may be more easily exchanged between eddies and the ambient fluid the escape of a float from an eddy can be identified from changes in the values of material tracers the authors identify a positive skewness in the time derivative of the buoyancy measured by the individual near surface floats as a indicator of convection in the presence of mesoscale eddies

elasticity of mgsio3 in the ilmenite phase abstract the single crystal elastic moduli of the ilmenite phase of mgsio 3 have been determined from brillouin spectroscopy they are c 11 472 c 12 168 c 33 382 c 13 70 c 44 106 c 14 27 c 66 152 and c 25 24 in gpa these elastic properties are consistent with a structural mechanical model where the silicon octahedra are very stiff under compression and shear this latter property yields an unexpectedly high shear modulus for the magnesium silicate ilmenite as compared with analogue compounds the further transformation to perovskite will probably be associated with a significant increase in elastic properties since the strong silicon polyhedra form a structural network in this phase the transformation of spinel and stishovite to ilmenite is associated with a slight density increase and a slight decrease in acoustic velocities this transformation will probably not produce a seismic discontinuity even if it does occur in the earth s mantle

karelian shungite an indication of 2 0 ga old metamorphosed oil shale and generation of petroleum geology lithology and geochemistry abstract the ca 2 0 ga old 600 m thick upper zaonezhskaya formation near lake onega nw russia contains unusually high concentrations of corg up to 98 averaging around 25 the formation contains an estimated 25 1010 tonnes of organic carbon accumulated within an area of 9000 km2 organic material is represented by shungite which forms a black dense amorphous or nanocrystalline mass consisting of c with traces of n o s and h autochthonous shungite occurs as disseminated organic material 0 1 50 corg which when mixed with migrated bitumen now pyrobitumen appears as coal like seams and lenses of semilustrous and semimat layer shungite rocks oil shales 50 75 corg the migrated bitumen originally petroleum represented by the lustrous vein and layer shungite conformably fills interbedding spaces or cross cutting joints and usually contains 80 98 corg the shungite bearing rocks of the upper zaonezhskaya formation represent one of the most richest accumulations of organic material reported from the palaeoproterozoic and one of the geologically earliest stages of petroleum generation the sediments of the zaonezhskaya formation were initially deposited in brackish water in a non euxinic lagoonal environment the high c s ratio 8 1000 with a zero intercept on the c s cross plot indicates that deposition occurred in sulphur poor water intensive synchronous volcanism may have contributed to both the enhanced delivery of nutrients and elevated sedimentation rate and eventually to the high degree of preservation of organic material the integrated data suggest that the organic material has a biogenic origin most likely algal or bacterial the organic material suffered complex catagenetic and metamorphic alteration which is reflected in 1 the four modal distribution of corg content with maxima at 5 30 65 and 95 2 highly variable 13 c org 45 to 17 3 bimodal distribution of 13 c org with maxima at 28 and 39 and 4 low h c ratios 0 005 0 2 abundant diagenetic carbonates associated with shungite rocks 13 c carb 5 to 26 and the presence of pyrite 34 s 22 to 31 reflects substantial loss of organic matter via bacterial reduction of sulphate during diagenesis the shungite rocks are characterised by a further substantial loss 50 of biologically produced organic material in the course of thermal maturation and by a depletion in 12 c 10 the isotopic composition of carbonate concretions does not indicate the involvement of fermentative diagenesis conservative estimates give 13corg of 34 as the best value of the initial biomass lustrous vein and layer shungite containing more than 80 corg are considered to be allochthonous migrated bitumen originally petroleum the semilustrous and semimat layer shungite rocks containing 55 75 corg represent oil shales with both migrated bitumen originally petroleum and autochthonous kerogen residues the oil source rocks were apparently hosted in the zaonezhskaya formation the generated oil has migrated both vertically and laterally with the highest concentration in cupola structures the locality at shunga represents the most significant volume of trapped petroleum from the study area

the search for fullerenes in rocks from the ries impact crater since their discovery fullerenes have been reported from various geological environments one group of these findings has been related to bolide impacts e g the sudbury crater and the k t and p t boundaries impact rocks of the ries crater germany including samples of suevites metamorphosed crystalline clasts and glass bombs have been collected in the otting altebrg and seelbronn quarries no fullerenes in concentrations above 1 ppb have been found in analyzed samples laser desorption time of flight mass spectrometry ld tof ms confirmed the absence of fullerenes in the analyzed samples these results support the concept that the ries impactor was a stony meteorite

thermodynamics of silicate liquids in the deep earth article i nfo we discuss the geophysical implications of recent first principles molecular dynamics simulations of mgsio3 liquid in particular the findings that the gruneisen parameter increases by a factor of three on two fold compression and the predicted melting curve the predicted melting temperature of mgsio3 perovskite at 136 gpa is 5400 600 k which if lowered by freezing point depression by 1300 k yields a mantle solidus temperature of 4100 k identical to recent estimates of the temperature at the base of the mantle we argue on this basis that partial melting at the base of the mantle is plausible while mgsio3 perovskite is denser than the isochemical liquid reasonable values of iron partitioning and bulk iron contents leads to the conclusion that a melt at the base of the multi component mantle would be denser than its surroundings and therefore buoyantly stable we predict the bulk sound velocity of this melt to be 10 9 km s 1 less than that of ultra low velocity zones and consistent with the explanation of these regions as being due to partial melting the increase on compression of the gruneisen parameter in the liquid state yields isentropes that are much hotter than previously thought a potential temperature of only 2450 k is sufficient to melt the entire mantle and a magma ocean will begin crystallization at mid mantle depths rather than at the base of the mantle

hydrothermal petroleum genesis migration and deposition in guaymas basin gulf of california hydrothermal activity and seabed mounds have been explored in guaymas basin by the deep sea drilling project dsdp piston coring dredging and diving with the deep submersible research vessel dsrv alvin sedimentary organic matter derived primarily from immature degraded microbial detritus is easily converted to petroleum under the hydrothermal regime these petroleums are mature and migrate in the fluids and by diffusion to the seabed the fluid migration is aided by near critical aqueous solution and supercritical carbon dioxide and hydrocarbons petroleum compositions vary from condensates to naphthenic to waxy all with significant amounts of asphaltenes and hydrothermal products such as olefins and toxic polynuclear aromatic hydrocarbons pah the heavy ends condense at the seabed depositing mainly as a cement with the sulfides and other minerals and to a lesser extent as entrapped oil and crystalline wax in vugs and conduits of the mounds the pah are high temperature resynthesis aromatiza

thermal expansion measurements at very high pressure systematics and a case for a chemically homogeneous mantle new data on thermal expansivity of iron to over 400 kbar in laser and electrically heated diamond anvil cells and on mgo and forsterite from spectroscopic data to over 200 kbar and previously measured adiabats boehler 1982 imply that at high pressure may be described by a constant value of 1n 1nv t 5 5 0 5 this behavior is supported by previous measurements at lower pressures on a large variety of materials densities of magnesio wustite and silicate perovskite in a pyrolitic ratio calculated at lower mantle conditions using a finite strain equation and at high pressures using the above systematics match those in prem through the entire lower mantle making a strong case for a uniform mantle

occurrence of natural fullerenes in low grade metamorphosed proterozoic shungite from karelia russia abstract we report on the occurrence of fullerenes in proterozoic shungite 2 ga from the shungite mine kondopoga karelia russia 62 12 n 34 17 e the presence of fullerenes has been confirmed by mass spectrometry with peaks at 360 and 720 amu atomic mass unit powder x ray diffraction showing ten diffraction peaks corresponding to the fullerite structure with a 1 4201 5 nm and 13 c nuclear magnetic resonance nmr spectroscopic studies showing a peak at 143 2 ppm in the kondopoga shungite mine fullerenes occur in silty shales that have experienced greenshist facies metamorphism

shock wave equation of state of enstatite shock compression data are reported for hot pressed bamble bronzite en 86 loaded to pressures between 104 and 161 gpa when compared to earlier shock wave data on en 90 at lower pressures and to static compression data our data require the presence of a phase change in p space the data yield two distinct trajectories which cannot be explained by experimental error the higher density data corrected for porosity and a small amount of metallic iron impurity agree with a theoretical en 86 high pressure phase hugoniot calculated from static compression equation of state data for perovskite pv structure silicates when experimental errors and uncertainties in the equation of state parameters are considered all the en86 data can be described by a calculated hugoniot if the first pressure derivative of the mgsio 3 pv bulk modulus is taken as 4 5 1 0 combining the present preferred data with recent shock wave data for single crystal forsterite we find that en 86 is slightly more dense than fo86 at pressures above 110 gpa comparison of the forsterite and enstatite data with the preliminary reference earth model prem lower mantle densities with corrections applied for the higher shock temperatures relative to lower mantle temperatures shows that prem densities are satisfied by olivine or pyroxene stoichiometries with mg mole fractions from 0 82 to 0 90 these values are lower than estimates of 0 90 to 0 95 developed from extrapolating static compression data to lower mantle conditions

temperature and salinity variability in heterogeneous oceanic convection abstract in regions of active oceanic convection such as the labrador sea small and mesoscale spatial variability is observed in the temperature and salinity fields t and s often t and s structures are density compensated with the density contribution of the s anomaly nearly equal and opposite to the contribution from the t anomaly this is manifest as variability in the spice field t s where and are the local expansion coefficients for t and s here the mechanisms for generating t and s variability by convection around a preexisting mesoscale eddy with particular attention to variability are investigated the authors perform several numerical experiments with identical density stratification mesoscale circulation and surface buoyancy forcing but with different combinations of t and s in the stratification and surface flux in all cases with both t and s variations present it is found that spice variability exceeds that of density in particular there are substantial heat

organic matter and the concentration of metals in precambrian stratiform deposits of the bohemian massif abstract organic matter is preserved in unmetamorphosed and low grade metamorphic pyrite and or mn bearing black shales pyrite mn stratiform ores cherts and siliceous stromatolites of proterozoic age in the barrandian area of the bohemian massif this organic matter consists mostly of kerogen with an isotopic composition and relative concentration of free radicals which depend on the metamorphic grade of the host rock 13 c pdb 30 7 to 36 9 nrel 0 161 to 0 132 enrichment of the kerogen in the light isotope of carbon a marked isotopic shift towards more positive 13c values with increasing metamorphic grade and the very low crystallinity of the incipient graphite lattice reflect the original aliphatic alicyclic character and algal origin of the kerogen its composition is similar to that of shungite chiefly aliphatic and alicyclic hydrocarbons were identified in the solvent extracts of these proterozoic rocks alkane patterns differ according to host rock type indicating their possible syngenetic origin other identifiable organic compounds amino acids carboxylic acids phenols and aromatic aldehydes are probably a result of later contamination the concentrations of u th v cr sb ag au zn and cu in pyrite and pyrite mn ores are relatively low in contrast stratiform concentrations of u v and chiefly au ag sb and zn are confined to siliceous stromatolites rich in kerogen or to adjacent jaspilites from a palaeogeographic viewpoint the highest concentrations of metals occur at the boundary between the oxidic facies stromatolites jaspilites and intercalations of other rocks and the reduced facies black shales where a syndiagenetic geochemical barrier developed mineralization was significantly influenced by subalkaline volcanism stromatolites of an intertidal type apparently formed where volcanoes rose to sea level stromatolitic breccias are intruded by chromium rich green quartz veins and locally covered by tuffs

role of organic matter in the proterozoic oklo natural fission reactors gabon africa of the sixteen known oklo and the bangombe natural fission reactors hydrothermally altered elastic sedimentary rocks that contain abundant uraninite and authigenic clay minerals reactors 1 to 6 at oklo contain only traces of organic matter but the others are rich in organic substances reactors 7 to 9 are the subjects of this study these organic rich reactors may serve as time tested analogues for anthropogenic nuclear waste containment strategies organic matter helped to concentrate quantities of uranium sufficient to initiate the nuclear chain reactions liquid bitumen was generated from organic matter by hydrothermal reactions during nuclear criticality the bitumen soon became a solid consisting of polycyclic aromatic hydrocarbons and an intimate mixture of cryptocrystalline graphite which enclosed and immobilized uraninite and the fission generated isotopes entrapped in uraninite this mechanism prevented major loss of uranium and fission products from the natural nuclear reactors for 1 2 b y 24 refs 4 figs

mechanisms of buoyancy transport through mixed layers and statistical signatures from isobaric floats idealized nonhydrostatic numerical calculations that resolve both plumes and geostrophic eddies are used to mimic isobaric float observations taken in the labrador sea deep convection experiment and study mechanisms of buoyancy transport through mixed layers the plumes and eddies are generated in a periodic channel initialized with a vertical profile of temperature and cooled by surface heat loss varying across the channel probability density functions and time series of vertical velocity and temperature computed from the floats are interpreted in terms of the kinematics of plumes and geostrophic eddies and their role in buoyancy transport estimates from eulerian time series from the numerical model suggest that geostrophic eddies and plumes have a comparable contribution to vertical heat flux

chemical stratification of the mantle formed by melting in the early stage of the terrestrial evolution abstract the accretional growth of the earth necessarily involved a molten zone in the outer layer magma ocean of the growing earth resulting in downwards extraction of the molten iron alloy i e core formation the primary stratification resulted from melting in the accretional stage of the earth and consisted of an fe core a perovskite rich lower mantle and a partially molten ultrabasic upper mantle in which the melt was concentrated in two regions near the surface of the cooling gravitational differentiation and crystallization in the magma ocean should give rise further to a finer stratification the upper mantle composed of two layers the upper olivine rich layer and the lower majorite garnet rich layer and the lower mantle with a perovskite rich composition both the 400 and 670 km discontinuities of the present mantle may be the chemical boundary the geophysical constraints of the mantle i e the seismic wave velocity and density profiles favor such a stratified mantle

metal silicate fractionation in the growing earth energy source for the terrestrial magma ocean based on the homogeneous accretion model of planets thermal evolution of the growing earth has been studied after the surface of the growing earth starts melting owing to the blanketing effect of the primordial atmosphere gravitational differentiation between metallic and silicate materials takes place in its upper region the differentiation would give rise to a large amount of gravitational energy release as well as layered structure inside the proto earth a part of released energy would be transported outward by convection considering the effects of gravitational fractionation and convection we have pursued numerically the evolution of the growing earth our results show that gravitational differentiation can supply energy large enough to keep the whole silicate layer in the molten state and that half of the released energy is conveyed outward by convective heat transport in the growing stage the temperature distribution in the silicate layer always lies between liquidus and solidus temperatures except in an uppermost thin zone the thermal structure obtained favors a notion of the primordial magma ocean and of chemical differentiation of mantle the structure of the growing earth which is composed of the central protocore the metallic layer and the silicate layer magma ocean would become gravitationally unstable and overturn to form a metallic core energy released by this overturn would not affect the structure of the upper magma ocean too much but undifferentiated primordial materials which come from the protocore would add to mantle materials through the overturn and this would help explain the isotopic mantle heterogeneity presently observed

origins of fullerenes in rocks this article is a technical comment and author response to the the discovery of naturally occuring fullerenes in shunga rock samples the commenting researchers did not find detectable amounts of fullerenes in a variety of carbon rich rocks they hypothesize that the fullerenes found in the shunga sample were probably a localized event the original researchers buseck and tsipursky provide a rebuttal with further comments including parallels to other minerological occurences all agreed that more data are needed 10 refs

extremal bounds on the seismic velocities in the earth s mantle summary based on global travel time constraints of the function p lee johnson the confidence region for the lower mantle p and s velocity profiles have been determined an exact method bessonova et al is used to compute the extremal bounds on velocity bounds on the lower mantle p velocity have an average resolution of 70 km in the depth range of 800 2900 km the average bound width is 0 14 km s 1 at the 97 per cent confidence level bounds on the lower mantle s velocity have an average resolution of 85 km in the depth range 850 2900 km and an average width of 0 13 km s 1 these results indicate that significant differences exist among the published velocity models and that the bounds can be used to discriminate among them the confidence regions are computed with an assumed upper mantle velocity model and are therefore subject to small baseline adjustments in velocity the introduction of approximate bounds on the upper mantle p increases the lower mantle bound width by 30 per cent for the p velocity in this case one obtains constraints on the absolute velocity function

silicate perovskite analogue scalo3 temperature dependence of elastic moduli abstract the elastic moduli of scalo 3 perovskite a very close structural analogue for mgsio 3 perovskite have been measured between 300 and 600 k using high precision ultrasonic interferometry in an internally heated gas charged pressure vessel this new capability for high temperature measurement of elastic wave speeds has been demonstrated on polycrystalline alumina the temperature derivatives of elastic moduli of al 2 o 3 measured in this study agree within 15 with expectations based on published single crystal data for scalo 3 perovskite the value of k s t p is 0 033 gpa k 1 and g t p is 0 015 gpa k 1 the relative magnitudes of these derivatives agree with the observation in duffy and anderson duffy t s anderson d l 1989 seismic velocities in mantle minerals and the mineralogy of the upper mantle j geophys res 94 1895 1912 that k s t p is typically about twice g t p the value of k s t p for scalo 3 is intermediate between those inferred less directly from v p t studies of fe free and fe and al bearing mgsio 3 perovskites wang y weidner d j liebermann r c zhao y 1994 p v t equation of state of mg fe sio 3 perovskite constraints on composition of the lower mantle phys earth planet inter 83 13 40 mao h k hemley r j shu j chen l jephcoat a p wu y bassett w a 1991 effect of pressure temperature and composition on the lattice parameters and density of mg fe sio 3 perovskite to 30 gpa j geophys res 91 8069 8079 zhang weidner d 1999 thermal equation of state of aluminum enriched silicate perovskite science 284 782 784 the value of g t p for scalo 3 is similar to those of most other mantle silicate phases but lower than the recent determination for mgsio 3 perovskite sinelnikov y chen g neuville d r vaughan m t liebermann r c 1998 ultrasonic shear wave velocities of mgsio 3 perovskite at 8 gpa and 800k and lower mantle composition science 281 677 679 combining the results from the previous studies and current measurements on scalo 3 perovskite we extracted the parameters q and 0 needed to fully specify its mie gruneisen debye equation of state in this study we have demonstrated that acoustic measurements of k s t unlike v p t data tightly constrain the value of q it is concluded that scalo 3 has normal 0 1 3 and high q 3 6 the high value of q indicates that scalo 3 has very strong intrinsic temperature dependence of the bulk modulus similar behaviour has been observed in measurements on fe and al bearing silicate perovskites mao et al 1991 zhang and weidner 1999

localization of deep ocean convection by a mesoscale eddy abstract observations of open ocean deep convection indicate that it is a highly localized phenomenon occurring over areas of tens of kilometers in diameter the cause of this localization has been ascribed to preconditioning the local weakening of the stable density stratification associated with upwardly domed isopycnal surfaces in a surface intensified cyclonic circulation however most numerical and laboratory studies of localized convection have prescribed the localization artificially by confining the surface buoyancy loss to a circular disk in contrast in the numerical simulations described here deep convection forced by horizontally uniform buoyancy loss is localized within a region of initially weaker stratification than its surroundings the preconditioned region is associated with a cold core cyclonic eddy in geostrophic and cyclostrophic balance as in previous studies of disk shaped cooling the localized convection region undergoes baroclinic instability at late times causing the br

mapping global d p velocities from isc pcp p differential travel times abstract we analyze 78 793 differential pcp p travel times reported by stations world wide to the international seismological centre isc during 1963 1987 to examine the seismic structure of the base of the mantle data were selected for earthquake station pairs within a 30 85 distance range and corrected for ellipticity and mantle path heterogeneity using the tomographic p velocity model iasp3d p of vasco et al 1994 j geophys res 99 13727 13755 the pcp p paths sample a very small number of regions of the base of the mantle limiting the amount of the lowermost mantle d that could be examined we find that the pcp p differential times are on average 0 49s greater than the times predicted by the iasp91 model of kennett and engdahl 1991 geophys j int 105 429 465 suggesting that that the mean p velocity within a 300 km thick d may be 0 35 slower than iasp91 for the regions sampled by our data we have attempted to create an image of some of the higher wavelength d heterogeneity to form a p wave comparison for the scs s and sscs ss study of wysession et al 1995a j geophys res 100 8351 we have therefore used the similar technique of converting the travel time residuals into velocity anomalies in the lowermost 300 km of the mantle and then stacking and smoothing them to create a geographical coherency plot for d lateral heterogeneity there are five regions with data coverage good enough to allow inferences about d p velocity structure relative to iasp91 1 velocities at least 0 9 1 2 fast beneath alaska 2 velocities at least 0 5 1 0 slow beneath hawaii 3 velocities 0 65 fast beneath northern asia our region of greatest coverage 4 a broad slow velocity region up to 3 0 beneath the western pacific and eastern asia 5 a complicated region of fast velocity 0 7 surrounded by two slow velocity regions 1 8 and 0 8 within d beneath central america the transition from slow to fast d velocities moving from beneath the western pacific ocean toward asia occurs in a different location for p velocities than for the s velocities of wysession et al 1995a

testing for fullerenes in geologic materials oklo carbonaceous substances karelian shungites sudbury black tuff comment and reply reply buseck et al s 1992 1 discovery of fullerenes in fractures in a shungite sample enclosed in diabase from russian karelia has been followed by several substantiating reports see buseck 2002 2 p 785 as well as by conflicting reports e g ebbesen et al 1995 3 mossman et al

the core mantle boundary the largest compositional discontinuity within the earth is the core mantle boundary cmb at a depth of 2889 km this boundary and the adjacent transition zones in the lowermost mantle and outermost core play a critical role in the earth s thermal and chemical evolution estimates of the heat flux out of the core indicate that the 200 km thick d region at the base of the mantle is a major thermal boundary layer the d region like its counterpart boundary layer in the lithosphere is laterally heterogeneous and possibly chemically stratified this complexity obscures the exact dynamic behavior of the d region however it is clear that the large density contrast 4 3 g em 3 across the cmb provides favorable con ditions for density stratification on both sides of the boundary the d region may be the refuse pile for heavy mantle heterogeneities while the outermost core may have a concentration of light components boundary layer instabilities in d have been invoked as sources of both localized mantle plumes and major upwelling currents in whole mantle convection systems dynamically supported topography on the cmb and lateral temperature gradients in d may produce coupling between the core and mantle influencing the excitation of the geodynamo the outer most core is generally believed to be radially and laterally homogeneous although chemical stratification has not been ruled out seismological geodynamical and geomagnetic investigations are unveiling the three dimensional complexity of the deep earth in the vicinity of the cmb

a giant palaeoproterozoic deposit of shungite in nw russia genesis and practical applications abstract occurrences of 2 0 ga mature organic material from the lake onega area nw russia constitute one of the most remarkable accumulations of organic carbon from the palaeoproterozoic the deposit occurs in a 1000 m sedimentary volcanic succession developed over an area of 9000 km 2 with an estimated total carbon reserve exceeding 25 10 10 tonnes the organic material occurs in the form of the mineraloid shungite which is a black non crystalline semi metallic material that contains 98 wt c the shungite bearing rocks were accumulated within a volcanic continental rift setting in a non euxinic brackish water lagoonal environment developed on the rifted margin of the archaean craton the occurrences of shungite bearing rocks represent a combination of a petrified oil field petrified organosiliceous diapirs and oil spills these are exemplified by three types of deposit i in situ stratified ii migrated diapirs and iii redeposited clastic in situ stratified deposits are composed of metamorphosed oil shales 80 wt c diapiric deposits form non stratified cupolas or mushroom shaped bodies composed of shungite containing 35 75 wt sio 2 and 20 55 wt c these are considered to represent organosiliceous rocks originally gels or mud the shungite rocks show abundant shrinkage cracks cryptic fluidal textures and brecciation caused by multiple fluidisation processes the current data are consistent with either diapiric or mud volcanic origins occurrences of clastic shungite are hosted by lacustrine volcanoclastic greywackes deposited from turbiditic flows shungite occurs in rocks as shungite has a heterogeneous molecular structure in which carbon occurs as 10 nm globules irregularly distributed within carbon showing no structure the unusual physicochemical and structural properties of shungite are used in diverse industrial and environmental applications including metallurgy water purification thermolysis and organosynthesis of cyclic hydrocarbons shungite is an effective sorbent for removal of organic and inorganic substances pathogenic bacteria and heavy metals from contaminated water

constraining the composition and thermal state of the mantle beneath europe from inversion of long period electromagnetic sounding data 1 we reexamine the problem of inverting c responses covering periods between 1 month and 1 year collected from 42 european observatories to constrain the internal structure of the earth earlier studies used the c responses which connect the magnetic vertical component and the horizontal gradient of the horizontal components of electromagnetic variations to obtain the conductivity profile of the earth s mantle here we go beyond this approach by inverting directly for chemical composition and thermal state of the earth rather than subsurface electrical conductivity structure the primary inversion parameters are the composition of the earth s mantle within the system cao feo mgo al2o3 sio2 and geotherm given these parameters we calculate mineral modes at the prevailing physical conditions and combine these with laboratory based models for the conductivity of individual minerals to estimate the bulk earth electrical conductivity structure from which c responses are calculated to further constrain the radial density profile we also invert for mass and moment of inertia the results agree with earlier geophysically derived conductivity and seismic velocity models and confirm that inversion of geophysical data for compositional parameters planetary composition and thermal state is feasible the inversion indicates most probable lower mantle geothermal gradients of 0 58 k km core mantle boundary temperatures of 2900 c bulk earth molar mg si ratios of 1 1 intermediate between the chondrite and pyrolite models and no significant change in mantle composition across the 670 km seismic discontinuity

organic geochemistry of precambrian shales and schists bohemian massif central europe abstract the composition and the structure of kerogens and subgraphitic materials from upper proteroic regionally metamorphosed black shales were investigated by different physico chemical method the isotopic composition of carbon changes with the intensity of the regional metamorphism kerogens from low grade metasediments have averaged 13 c values 35 kerogens from chlorite and biotite zones 31 samples display high diversity of primary sedimentary materialos details were obtained using transmission electron microscopy tem crystalline order improves with the intensity of the regional metamorophism turbostratic carbonacveous matter is described from low grade metasediments graphite occurs at the end of the biotite zone however both metallogenetic and contact metamorphic processes can be involved in some samples the second form of graphite has been identified probably of detrital origin inherited from some high grade metamorphic area existing at the time of sedimentation of primary rocks

petrography and paragenesis of organic matter associated with the natural fission reactors at oklo republic of gabon a preliminary report sixteen known uranium rich pockets in the sediment hosted uranium ore deposits in the oklo area became nuclear fission reactors 1968 50 ma ago and operated as such for up to 1 ma nuclear criticality was caused by unique and fortuitous geological environments and events these included the localized high concentrations of uranium in small pockets in the ore bodies the fact that the relative abundance of the fissile 235u isotope was five times greater in uranium 2 ga ago than present the presence of water which acted as a moderator in the natural reactors and the absence of neutron poisons which are elements that can prevent nuclear chain reactions organic matter is present in all of the oklo natural reactors but it is abundant only in reactors 7 to 16 organic matter has been studied in natural reactors 7 to 9 and at locations at various distances from these reactors bitumen in the oklo reactors is the predominant organic phase it is now solid bitumen containing dispersed cryptocrystalline graphite in crystal domains smaller than optical microscopic size its immediate precursor was liquid bitumen generated from syngenetic kerogen in organic rich sedimentary rocks in the francevillian basin of gabon and in the natural reactors themselves by hydrous reaction mechanisms prior to during and after nuclear criticality a preliminary paragenesis of organic matter at oklo may be defined through the following sequence of events a protokerogen and kerogen evolve from abundant cyanobacteria in the tidal and deltaic sediments in the basal fa formation of the francevillian series during sedimentation and burial respectively b during subsequent subsidence of the basin the first generation of bitumen and petroleum occurred c during uplift the sedimentary strata were fractured and bitumen and petroleum migrated through fractures following this oxidizing aqueous solutions carrying uranyl ions migrated through the highly fractured rocks met and were reduced by organic matter and precipitated pitchblende or uraninite at the present sites of the oklo uranium ore deposits and natural reactors the natural reactors reached nuclear criticality they were heated and produced the second generation of bitumen through hydrous reactions from the by now solid first generation bitumen and remaining kerogen finally hydrothermal effects associated with the dolerite dike swarm intrusion 750 150 ma ago produced yet another localized generation of liquid bitumen from solid organic matter possibly other bitumen generations also occurred during and following this time interval the organic matter in the natural reactors soon became a solid and was able to prevent the loss of uraninite grains enclosed in it these uraninite grains trapped and then immobilized fission products until and to an extent even after a major tectonic igneous event the intrusion of the dolerite dike swarm

stability of mg fe sio3 perovskite and the structure of the lowermost mantle thermodynamic analysis shows that mg fe sio3 perovskite is stable throughout the likely pressure temperature and compositional regime of the earth s mantle the breakdown of perovskite to its constituent oxides appears unlikely even under the extreme conditions of the core mantle boundary this reaction had been proposed to reconcile estimates of silicate melting with seismic observation and proposed geotherms

nonfractional crystallization of a terrestrial magma ocean it has been suggested that evolution of a terrestrial magma ocean does not unavoidably follow a fractional crystallization scenario convection is able to preclude differentiation until a sharp viscosity increase occurs near some critical crystal fraction however this kind of crystallization and its physical and chemical consequences have not been previously studied we consider an end member called here nonfractional crystallization we begin with a simple equilibrium thermodynamical model of partial melts which is based on an ideal three component phase diagram it allows a self consistent calculation of physical and chemical parameters in the melting range at all interesting pressures in particular adiabats of the convecting magma ocean are calculated the sharp increase in the viscosity is supposed to occur near the maximum packing crystal fraction however almost independently of this value convection occurs even in the highly viscous quasi solid part of the magma ocean and it is strong enough to prevent differentiation in deep regions a kind of compositional convection occurs due to the layered differentiation although it is weaker than the thermal convection only a surface region undergoes an essential differentiation via melt expulsion by compaction the thickness of this layer depends on the rheology of partial melts critical crystal fraction and crystal sizes but in any case the basal pressure hardly can exceed 5 10 gpa because of lower pressures in the moon the thickness of the differentiating layer is large and thus the entire lunar magma ocean could undergo a strong differentiation remelting due to the energy released by differentiation is crucial only for much deeper layers possibly deeper than about 1000 km for the earth for the remaining shallow layer p 5 10 gpa the predicted increase of the melt fraction is less than 40 at the surface and decreases to zero at the bottom of the differentiating layer thus the nonfractional crystallization is suggested to be a likely alternative to the fractional crystallization the crucial and still poorly understood factors are suspension in convective layers rheology of partial melts crystal size and surface conditions the most pronounced chemical consequence of the nonfractional crystallization is an almost completely preserved undifferentiated lower mantle and possibly a significant undifferentiated part of the upper mantle at all depths in the beginning of differentiation not only the first liquidus solid phase but also subsequent phases have been partially crystallized so when the differentiation begins it involves mixtures of phases it is important for the remaining layer where differentiation is unavoidable this layer does not have as strong differentiation of minor elements as in the case of fractional crystallization but it will still involve differentiation of major elements future geochemical calculations of this multiphase differentiation considering both major and minor elements could help to constrain the differentiation further

adiabats of quartz coesite olivine and magnesium oxide to 50 kbar and 1000 k and the adiabatic gradient in the earth s mantle the adiabats of olivine magnesium oxide and quartz were measured up to 50kbar and 1000 k an end loaded piston cylinder apparatus with an in situ pressure gauge and a very fine thermocouple was used to measure t p s during adiabatic compression a power law between t p s and compression yields values of the power n ln t p s ln that agree with previous results from salts metals and fluids assuming constant values for n the adiabtic gradient for an olivine upper mantle and a magnesium oxide lower mantle was calculated the results agree well with some previous theoretical estimates the volume dependence of the gruneisen parameter was calculated from the thermodynamic equation ln ln b p n where b is the isothermal bulk modulus is found to a good approximation to be proportional to volume table 6 is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j82 002 1 00 payment must accompany order

observations of open ocean deep convection in the labrador sea from subsurface floats abstract the occurrence and extent of deep convection in the labrador sea in winters 1996 97 and 1997 98 is investigated from measurements of over 200 neutrally buoyant subsurface profiling autonomous lagrangian circulation explorer palace and sounding oceanographic lagrangian observer solo floats in addition to providing drift velocity data and vertical profiles of temperature and salinity 55 floats are equipped with vertical current meters vcms time series of vertical velocity derived from measured pressure and vertical flow past the float and temperature are obtained from the vcm floats mixed layer depths estimated from profile measurements indicate that convection reached depths greater than 1300 m in 1997 but no deeper than 1000 m in 1998 deep mixed layers were concentrated in the western basin although a number of deep mixed layers were observed southwest of cape farewell and also north of 60 n the highest variance in vertical velocity and the lowest mean temperatures were found in t

measurement of the melting curve of mg0 9fe0 1sio3 at lower mantle conditions and its geophysical implications an experimental determination of the melting of mg0 9fe0 1sio3 under lower mantle conditions is presented samples were compressed and laser heated nd yag in a mao bell type diamond cell the temperature fields generated in the sample are measured using a simple tomographic technique and spectroradiometer mg0 9fe0 1sio3 in the perovskite structure melts at 3000 300 k independently of pressure over the range of 22 65 gpa the melting curve of mg0 9fe0 1sio3 represents an experimental upper bound upon the geotherm from 700 to 1500 km this melting curve corresponds to a homologous temperature of 0 70 or 0 85 for one or two layer mantle convection respectively this is consistent with either one or two layer mantle convection and a lower mantle of constant viscosity based upon homologous temperature arguments

carbonaceous substances associated with the paleoproterozoic natural nuclear fission reactors of oklo gabon paragenesis thermal maturation and carbon isotopic and trace element compositions field relationships textural and reflectance characteristics and carbon isotopic compositions indicate that at least eight different categories of carbonaceous substances cs occur in the black shales uranium ores and fossil nuclear fission reactors of oklo the categories include kerogens of the mikouloungou coal in the fa formation the c1 pelites of the fa formation the black shale of the fb formation and bitumens present in veinlets in the basal black shale of the fb formation in the fa formation in normal ore and in hydraulic fractures in and near the fossil reactors and in late dolerite dikes bitumen migration occurred at oklo during at least three intervals 1 ca 2 0 ga ago when petroleum liquids derivatives of which are preserved as solid bitumen were generated by thermal maturation of black shale kerogen 2 ca 1 968 50 ma ago when 15 or more pockets of uranium ore achieved criticality and 3 977 to 981 27 ma ago when dolerite dikes intruded radionuclide migration occurred during intervals 2 and 3 bitumenization trends established for organic matter which has undergone thermal maturation fail to discriminate between heat affected and normally matured cs at oklo in and near oklo reactors where several types of solid bitumen commonly occur in close association carbon of the youngest low reflectance bitumen is isotopically heavier than that of older high reflectance bitumen due to thermal cracking this process together with enhanced radiolysis of bitumen in and near the reactors have combined to increase its 13c avg 25 8 compared to that of bitumen samples in normal ore avg 35 5 distant from the reactors graphitized bitumen inhibited migration of 235u and some fission products in uraninite of the natural reactors however alkaline earth elements such as ba sr and mo and alkaline elements rb and cs not compatible in the uo2 crystalline structure have migrated in hydrothermal solutions and in the once fluid oklo bitumens in situ analysis of solid bitumens by laser ablation icp ms detects differences in trace element composition developed as a result of their varying geological histories and evolutionary trends

petrology and genesis of karelian shungite high rank coal abstract shungites are highly carbonaceous highly metamorphosed rocks associated with several stratigraphic levels of the lower proterozoic in karelia being a complex material shungite is very important also as oldest accumulations of concentrated organic matter the nature of shungite is still unclear despite its more than a century long study by russian and western scientists a chemical coal petrographic study of shungite has been conducted using a specially designed technique the etching of polished surfaces it is found that the shungite bed near shunga village is a coal seam with a typical set of megascopic features rather than an accumulation of bitumen this bed consists not only of sapropelic but of humic organic matter as well unlike other biogenic structures from precambrian coal such as the huron series michigan lake the structures established in shungite near shunga village have a more complex plant composition organic matter from various types of shungite bearing rocks show different petrographic and chemical properties thus organic matter of sapropelic nature from silicate rocks with traces of stromatolite texture differs from the coal matter composing the shunga bed shungites are the most metamorphosed coals among all those known at present and they are assigned here to metaanthracite rank the results obtained show a new insight into the biogenic remains composing an ancient coal bed and in terms of the present stratigraphic scale allow the beginning of coal accumulation to be placed in the proterozoic although the possibility of a non precambrian age cannot be ruled out

geological fullerenes review and analysis abstract fullerenes have been reported from numerous terrestrial and meteoritic sources but only at low concentrations the occurrences are associated with localized energetic events such as lightning impacts of extraterrestrial objects and wildfires great interest has also been generated by a series of papers that report noble gases with anomalous isotopic compositions encapsulated within fullerenes in spite of all of the published work many unresolved questions remain about the identity and formation of fullerenes in geological environments

testing for fullerenes in geologic materials oklo carbonaceous substances karelian shungites sudbury black tuff comment and reply the presence of low concentrations of fullerenes has been reported from numerous terrestrial and meteoritic sources buseck 2002 1 in a recent paper mossman et al 2003 2 present mass spectra of carbonaceous substances using laser desorption ionization ldi and high resolution electron

fully lagrangian floats in labrador sea deep convection comparison of numerical and experimental results measurements of deep convection from fully lagrangian floats deployed in the labrador sea during february and march 1997 are compared with results from model drifters embedded in a large eddy simulation les of the rapidly deepening mixed layer the deep lagrangian floats dlfs have a large vertical drag and are designed to nearly match the density and compressibility of seawater the high resolution numerical simulation of deep convective turbulence uses initial conditions and surface forcing obtained from in situ oceanic and atmospheric observations made by the r v knorr the response of model floats to the resolved large eddy fields of buoyancy and velocity is simulated for floats that are 5 g too buoyant as well as for floats that are correctly ballasted mean profiles of potential temperature lagrangian rates of heating and acceleration vertical turbulent kinetic energy tke vertical heat flux potential temperature variance and float probability distribution functions pdfs are compared for actual and model floats horizontally homogeneous convection as represented by the les model accounts for most of the first and second order statistics from float observations except that observed temperature variance is several times larger than model variance there are no correspondingly large differences in vertical tke heat flux or mixed layer depth the augmented temperature variance may be due to mixing across large scale temperature and salinity gradients that are largely compensated in buoyancy the rest of the dlf statistics agree well with the response of correctly ballasted model floats in the lowest 75 of the mixed layer and are less consistent with results from buoyantly ballasted model floats other differences between observation and simulation in the mean profiles of heat flux vertical tke and lagrangian heating and vertical acceleration rates are confined to the upper quarter of the mixed layer these differences are small contributions to layer averaged quantities but represent statistically significant profile features larger observed values of heat flux and vertical tke in the upper quarter of the mixed layer are more consistent with model floats ballasted light float buoyancy however cannot fully account for the observed pdfs temperature profiles and lagrangian rates of heating and acceleration a test of lagrangian self consistency comparing vertical tke and lagrangian acceleration also shows that dlf measurements are not significantly affected by excess float buoyancy these upper mixed layer features may instead be due to the interaction of wind driven currents and baroclinicity

evidence for fullerenes in solid bitumen from pillow lavas of proterozoic age from mitov bohemian massif czech republic abstract andesitic pillow lavas containing biogenic solid bitumen sb are a constituent of a neoproterozoic volcanosedimentary sequence tepla barrandian unit bohemian massif in the mitov area of the czech republic a black shale formation that is crosscut by these andesitic basalts is 565 ma old carbon disulfide extracts of two powdered samples of sb contain 0 2 and 0 3 ppm of c 60 respectively as determined by high pressure liquid chromatography the peak assignment based on retention time is fully supported by high resolution electron ionization mass spectrometry ei ms no c 70 was detected nor was c 60 found in two other sb samples from this locality other investigated carbonaceous samples from bohemia coals and anthracites of upper paleozoic age and anthraxolite graphitoids and graphite of upper proterozoic age did not contain fullerenes at concentrations above the detection limit of 0 01 ppm the absence of c 60 in these samples was confirmed by ei ms the proposed mechanism of fullerene formation involves a primary algal phase generation of a hydrocarbonaceous mixture in the course of thermal evolution of the sedimentary series and their high temperature transformation related to the extrusion of basalt an important feature for fullerene conservation was the enclosure of fullerenes in sb with a structure similar to glasslike carbon where the fullerene was protected against oxidation

melting of garnet peridotite to 13 gpa and the early history of the upper mantle by analogy with the evolution of the moon it has been suggested that the earth may have had a magma ocean or liquid outer layer before 3 800 myr ago 1 its presence would have had profound implications for the primary stratification of the mantle into upper mantle transition zone and lower mantle2 3 an essential constraint on this hypothesis is a knowledge of the high pressure melting characteristics of mantle material generally assumed to be peridotite in the upper mantle we recently described4 the first melting experiments on mantle peridotite to 14 gpa using spinel iherzolite klb 1 from kilbourne hole new mexico we showed that partial melts close to the solidus at 5 7 gpa are komatiitic in composition and that the solidus and liquidus converge at high pressures here we report further melting experiments on garnet iherzolite phn1611 from thaba putsoa lesotho we confirm the convergence of the solidus and liquidus and we show a negative dt dp slope for the liquidus above 7 gpa these observations are briefly discussed in terms of their importance to the petrological evolution of the upper mantle and the presence of a magma ocean in the early archaean

effect of anigneous intrusion on oil shale at rundle australia abstract elemental analyses x ray diffraction thermal and isotopic analyses gas chromatography mass spectrometry electron spin resonance nuclear magnetic resonance spectroscopy and demineralizing techniques have been used to evaluate the effect of a small igneous intrusion on rundle oil shale each set of results contributes to an overall appreciation of how in situ pyrolysis of a highly aliphatic kerogen occurs as in previous studies application of a range of methods gives a better understanding than any of the techniques on its own significant conclusions are as follows 1 the shale samples closest to the intrusion contain the least organic matter 2 a micro reservoir for expelled volatiles was identified 1 m below the intrusion 3 the hydrogen deficient carbonaceous residue remaining close to the intrusion produces no oil on further heating and 4 the major effect of the intrusive event was the in situ pyrolysis of the oil shale the severity of alteration decreasing with distance from the contact

the evolution of the onaping formation at the sudbury impact structure the 1 4 1 6 km thick onaping formation consists of a complex series of breccias and melt bodies lying above the sudbury igneous complex sic at the sudbury impact structure based on the presence of shocked lithic clasts and various glassy phases the onaping has been described as a suevitic breccia with an origin at least in part as fallback material recent mapping and a redefined stratigraphy have emphasized similarities and differences in its various vitric phases both as clast types and discrete intrusive bodies the nature of the onaping and that of other suevitic breccias overlying impact melt sheets is reviewed the relative thickness internal stratigraphic and lithological character and the relative chronology of depositional units indicate multiple processes were involved over some time in the formation of the onaping the sudbury structure formed in a foreland basin and water played an essential role in the evolution of the onaping as indicated by a major hydrothermal system generated during its formation taken together observations and interpretations of the onaping suggest a working hypothesis for the origin of the onaping that includes not only impact but also the interaction of sea water with the impact melt resulting in repeated explosive interactions involving proto sic materials and mixing with pre existing lithologies this is complicated by additional brecciation events due to the intrusion of proto sic materials into the evolving and thickening onaping fragmentation mechanisms changed as the system evolved and involved vesiculation in the formation of the upper two thirds of the onaping

dynamics of a phase change at the base of the mantle consistent with seismological observations the phase change model for the origin of the d seismic discontinuity is tested by comparing the results of convection modeling with seismic observations we compute a number of global dynamic models that incorporate a phase change at the base of the mantle with different characteristics and transform the resulting temperature field and the distribution of phases to seismic velocities over 900 two dimensional synthetic waveforms are computed for each of the models from which s scs and scd phases are picked the distribution of the relative amplitudes and differential travel time residuals for these phases are statistically compared with the distribution of data from four well studied regions northern siberia alaska india and central america in a search for the characteristics of a phase transition that best match these seismic observations we find that the best fit among the models considered is obtained for phase transitions characterized by a clapeyron slope of 6 mpa k 1 and an elevation above the core mantle boundary of 150 km under adiabatic temperature or 127 gpa and 2650 k on a p t diagram dynamic models demonstrate that the value of clapeyron slope and the density difference between the phases can have significant influence on the dynamics of plumes but probably only a minor influence on the dynamics of subducted slabs we find that the thermal structure of subducted slabs can be important in giving rise to the seismic triplication the strongest scd arrivals in our models are observed in the area of subduction the folding of the slab at the base of the mantle leads to patterns in differential travel time distributions consistent with seismic observations and suggests that the largest heterogeneity occurs at the top of the d layer or just above it analysis of the spatial autocorrelation functions of the differential travel time residuals suggests that their characteristic peaks reflect the patterns of slab folding and may provide constraints on the rheology of slabs at the base of the mantle

nanominerals and ultrafine particles in sublimates from the ruth mullins coal fire perry county eastern kentucky usa abstract mineral sublimates from the ruth mullins fire in abandoned underground and surface mines in the high volatile a bituminous middle pennsylvanian hazard no 7 coalbed perry county kentucky were examined by optical mineralogy x ray diffraction xrd and high resolution transmission electron microscopy hr tem optical examination revealed the presence of salammoniac and a fine unidentified fibrous mineral xrd also showed the presence of salammoniac along with trace amounts of quartz kaolinite and possibly phengite both cubic and dendritic salammoniac forms were observed with hr tem gypsum jarosite with cubic pseudomorphs after pyrite and fe minerals including cr bearing hematite in association with jarosite were observed with hr tem dehydration of jarosite can lead to the formation of less hydrous fe sulfates and hematite

geochemical markers of the cretaceous tertiary boundary event at brazos river texas usa the cretaceous tertiary boundary sites around the gulf of mexico are close to the chixculub impact site and are relatively well studied yet much remains to be learned about them therefore the first integrated study of carbon soot and fullerenes in a cretaceous tertiary boundary section was undertaken at the brazos 1 site on the brazos river in texas at the most complete section of end cretaceous and basal paleocene deposits on the texas segment of the gulf coast area up to 409 ppm of native sulfur so were serendipitously discovered in a spherule bearing unit of the br 1 section and lesser amounts were found in spherule bearing units of nearby brazos riverbed sections in a section on darting minnow creek the isotopic composition 33s 12 97 34s 24 89 and 36s 46 4 implies that this so cannot have come to earth by the impactor that formed the chicxulub crater but most likely was produced by sulfate reducing bacteria during a local transient bacterial bloom for which the sulfate was provided by caso4 bearing spherules carbon and soot were determined in twelve samples representing all units of br 1 from the cretaceous corsicana kemp formation to the tertiary kincaid formation a significant increase of c and soot contents up to 2 2 104 ppm and 1 4 104 ppm respectively occurs in a sandy bed at the top of the kt complex fullerenes were determined in fifty four samples from all units of the same br 1 section less than 1 ppb was reliably detected at the same sandy bed where the strongest ir anomaly of the section is known to occur it is suggested here that the chicxulub impact 65 ma ago ignited local wildfires that produced c soot and fullerene which settled onshore or near shore whence they were transported to the brazos site by coastal flooding and associated sediment laden water plumes moving offshore

fundamental thermodynamic relations and silicate melting with implications for the constitution of d we describe fundamental thermodynamic relations helmholtz free energy as a function of volume and temperature for solids and liquids simple physically based expressions which contain all thermodynamic information about a system the solid fundamental relation consists of debye and birch murnaghan finite strain theory combined in the mie gruneisen framework the liquid fundamental relation is derived by taking the high temperature limit of the solid expression we derive the liquid equation of state which contains only four parameters from the liquid fundamental relation and show that it successfully describes measurements of liquid alkali metals water and liquid diopside over a wide range of pressure and temperature we find optimal fundamental relation parameters for diopside enstatite ilmenite and perovskite and find the solid relation to be in excellent agreement with data including heat capacities thermal expansion and mgsio3 phase equilibria we then combine the liquid and solid fundamental relations to calculate the melting curves of diopside enstatite and perovskite which are found to be in excellent agreement with experiment all predicted melting curves have dt dp slopes which decrease steadily with pressure eventually becoming negative because of liquid crystal density inversion our predicted melting temperature of perovskite in the d region 3750 k at the base of the mantle is thousands of degrees lower than previous estimates yet it is consistent with experimental data the predicted melting curve although consistent with the lack of widespread melting in the lower mantle is much lower than recently proposed geotherms in the d layer at the base of the mantle by combining our results with seismic observations of the deep mantle we propose that the d layer consists of magnesiowustite and silica in the form of stishovite or its recently discovered high pressure modification

black carbon in soils and sediments analysis distribution implications and current challenges this review highlights the ubiquity of black carbon bc produced by incomplete combustion of plant material and fossil fuels in peats soils and lacustrine and marine sediments we examine various definitions and analytical approaches and seek to provide a common language bc represents a continuum from partly charred material to graphite and soot particles with no general agreement on clear cut boundaries formation of bc can occur in two fundamentally different ways volatiles recondense to highly graphitized soot bc whereas the solid residues form char bc both forms of bc are relatively inert and are distributed globally by water and wind via fluvial and atmospheric transport we summarize chronologically the ubiquity of bc in soils and sediments since devonian times differentiating between bc from vegetation fires and from fossil fuel combustion bc has important implications for various biological geochemical and environmental processes as examples bc may represent a significant sink in the global carbon cycle affect the earth s radiative heat balance be a useful tracer for earth s fire history build up a significant fraction of carbon buried in soils and sediments and carry organic pollutants on land bc seems to be abundant in dark colored soils affected by frequent vegetation burning and fossil fuel combustion thus probably contributing to the highly stable aromatic components of soil organic matter we discuss challenges for future research despite the great importance of bc only limited progress has been made in calibrating analytical techniques progress in the quantification of bc is likely to come from systematic intercomparison using bcs from different sources and in different natural matrices bc identification could benefit from isotopic and spectroscopic techniques applied at the bulk and molecular levels the key to estimating bc stocks in soils and sediments is an understanding of the processes involved in bc degradation on a molecular level a promising approach would be the combination of short term laboratory experiments and long term field trials

oily old ores evidence for hydrothermal petroleum generation in an archean volcanogenic massive sulfide deposit oil is formed in some modern seafloor vent systems after rapid thermal maturation of sedimentary organic matter by hydrothermal fluids although most of this petroleum escapes into the ocean some hydrocarbons may be trapped as fluid inclusions in hydrothermal precipitates or as bituminous residues in cavities however the geological record lacks evidence of this phenomenon which is unfortunate because it could be significant for understanding the history of petroleum genesis the processes of hydrothermal mineralization and perhaps the origin and early evolution of life from the pilbara craton of australia we report the discovery of pyrobitumen and oil in an early archean ca 3235 ma deep sea volcanogenic massive sulfide deposit the oil occurs in fluid inclusions within hydrothermal barite and pyrobitumen is intergrown with polymetallic sulfides petrographic textures show that the oil was emplaced and thermally altered coked before late stage sulfide mineralization the results demonstrate that subseafloor hydrothermal petroleum generation was active during the early archean possibly providing an energy and carbon source for a subsurface microbiota metabolizing hydrothermal sulfur species

thermal alteration of cretaceous black shale by diabase intrusions in the eastern atlantic ii effects on bitumen and kerogen abstract the thermal effects of three one major and two minor miocene diabase intrusions on cretaceous black shales from dsdp site 41 368 have been analyzed a concentration gradient was observed especially for the hydrocarbons decreasing towards the major intrusion and between the three sills the thermally altered samples in the proximity of and between the sills contained elemental sulfur and an excess of thermally derived pristane over phytane whereas the unaltered sediments contained no elemental sulfur and more phytane than pristane a maximum yield of the extractable hydrocarbons was observed at a depth of 7 m below the major sill two classes of molecular markers were present in this bitumen suite the first was sesqui di and triterpenoids and steranes which could be correlated with both terrigenous and autochthonous sources they were geologically mature and showed no significant changes due to the thermal stress the second class was found in the altered samples which contained only polynuclear aromatic hydrocarbons with low alkyl substitution and sulfur and oxygen heterocyclic aromatic compounds these compounds were derived from pyrolytic reactions during the thermal event kerogen was isolated from all of these samples but only traces of humic substances were present the h c n c 13 c 34 s and d all exhibit the expected effects of thermal stress the kerogen becomes more aromatized and richer in 13c 34s and d in the proximity of and between the sills maturation trends were also measured by the vitrinite reflectance and electron spin resonance where the thermal stress could be correlated with an elevated country rock temperature and an increased degree of aromaticity the effects of in situ thermal stress on the organic rich shales resulted in the generation and expulsion of petroliferous material from the vicinity of the sills

the younger dryas impact hypothesis a requiem abstract the younger dryas yd impact hypothesis is a recent theory that suggests that a cometary or meteoritic body or bodies hit and or exploded over north america 12 900 years ago causing the yd climate episode extinction of pleistocene megafauna demise of the clovis archeological culture and a range of other effects since gaining widespread attention in 2007 substantial research has focused on testing the 12 main signatures presented as evidence of a catastrophic extraterrestrial event 12 900 years ago here we present a review of the impact hypothesis including its evolution and current variants and of efforts to test and corroborate the hypothesis the physical evidence interpreted as signatures of an impact event can be separated into two groups the first group consists of evidence that has been largely rejected by the scientific community and is no longer in widespread discussion including particle tracks in archeological chert magnetic nodules in pleistocene bones impact origin of the carolina bays and elevated concentrations of radioactivity iridium and fullerenes enriched in 3 he the second group consists of evidence that has been active in recent research and discussions carbon spheres and elongates magnetic grains and magnetic spherules byproducts of catastrophic wildfire and nanodiamonds over time however these signatures have also seen contrary evidence rather than support recent studies have shown that carbon spheres and elongates do not represent extraterrestrial carbon nor impact induced megafires but are indistinguishable from fungal sclerotia and arthropod fecal material that are a small but common component of many terrestrial deposits magnetic grains and spherules are heterogeneously distributed in sediments but reported measurements of unique peaks in concentrations at the yd onset have yet to be reproduced the magnetic grains are certainly just iron rich detrital grains whereas reported yd magnetic spherules are consistent with the diffuse non catastrophic input of micrometeorite ablation fallout probably augmented by anthropogenic and other terrestrial spherular grains results here also show considerable subjectivity in the reported sampling methods that may explain the purported yd spherule concentration peaks fire is a pervasive earth surface process and reanalyses of the original yd sites and of coeval records show episodic fire on the landscape through the latest pleistocene with no unique fire event at the onset of the yd lastly with yd impact proponents increasingly retreating to nanodiamonds cubic hexagonal lonsdaleite and the proposed n diamond as evidence of impact those data have been called into question the presence of lonsdaleite was reported as proof of impact related shock processes but the evidence presented was inconsistent with lonsdaleite and consistent instead with polycrystalline aggregates of graphene and graphane mixtures that are ubiquitous in carbon forms isolated from sediments ranging from modern to pre yd age important questions remain regarding the origins and distribution of other diamond forms e g cubic nanodiamonds in summary none of the original yd impact signatures have been subsequently corroborated by independent tests of the 12 original lines of evidence seven have so far proven to be non reproducible the remaining signatures instead seem to represent either 1 non catastrophic mechanisms and or 2 terrestrial rather than extraterrestrial or impact related sources in all of these cases sparse but ubiquitous materials seem to have been misreported and misinterpreted as singular peaks at the onset of the yd throughout the arc of this hypothesis recognized and expected impact markers were not found leading to proposed yd impactors and impact processes that were novel self contradictory rapidly changing and sometimes defying the laws of physics the yd impact hypothesis provides a cautionary tale for researchers the scientific community the press and the broader public

thermodynamically consistent decompression implications for lower mantle composition estimates of the composition of the lower mantle are commonly obtained by a process of adiabatic decompression in which zero pressure mantle parameters are determined with a least squares fit of an equation of state to mantle densities we show that this procedure may lead to biased estimates of the zero pressure density and compressibility of the mantle the bias can be eliminated or minimized by subjecting the equation of state fit to a thermodynamic constraint at zero pressure such inversions provide equations of state that are compatible with the lower mantle as well as the thermal properties of selected mineral models we used this method to evaluate assemblages containing mg fe sio3 perovskite and mg fe o with fe fe mg ratios as high as 0 2 thermodynamic systematics were used to place bounds on the anderson gruneisen parameter s for perovskite we find a fairly large range of acceptable models for the composition of the lower mantle they range from uppermantle like compositions to assemblages that are enriched in both si and fe relative to the upper mantle however a pure perovskite lower mantle whether enriched in fe or not seems improbable small fe enrichments of the order of 1 given density contrasts across the 670 km discontinuity that are probably insufficient to prevent convective mixing of the upper and lower mantles we therefore suggest that unless the mantle is homogeneous in its major oxide components the lower mantle is likely to be enriched in fe by at least several percent

fullerenes found in the permo triassic mass extinction period fullerenes have been identified by high performance liquid chromatography with uv visible spectroscopic analysis of toluene extracts of deep sea claystones from permo triassic p t boundary sections in the inuyama area central japan the analysis reveals the presence of 10 20 parts per trillion of c60 only in the dark colored rock samples suggesting the anoxia at the time of the p t boundary 250 million years ago when the greatest phanerozoic mass extinction occurred the fullerenes were likely synthesized within locally anoxic zone in the extensive wildfires on the supercontinent pangea and deposited on an anoxic deep sea floor of the superocean panthalassa

melt segregation from partially molten source regions the importance of melt density and source region size the compressibility of basic melt at 1 atmosphere is about an order of magnitude higher than that of mantle minerals consequently the density contrast between melt and the principal residual crystals in mantle source regions is expected to decrease with increasing source region depth the increasingly olivine normative character of primary melts produced at greater depths is also expected to result in a decrease in this density contrast with increasing source region depth once vertical permeability is established by melt generated during partial melting buoyancy driven melt percolation can under some circumstances segregate melt from the residual crystals in its source region on a geologically rapid time scale limits to this process are provided by cooling of the source region freezing melt in and rigidity of the crystalline matrix mechanically trapping melt source region size influences these limits strongly consequently small partially molten diapirs km in diameter may be able to trap large melt fractions 30 but larger source regions would be unable to do so the reduction in density contrast with pressure reduces the buoyant force driving melt percolation and provides another limit to melt segregation diapirs at depth may thus stably contain large fractions of melt but may decompress and unload their melt during ascent this effect would be enhanced in small diapirs and may be relevant to the genesis of komatiitic magma melt compression may also be a factor in explaining why the very different maximum depths inferred for typical basic melt segregation from source regions on different planets 500 km on the moon 250 km on mars 100 km on earth correspond to similar pressures 25 35 kbar at greater pressures melt may no longer be capable under ordinary conditions of segregating upwards by buoyancy this may also help to explain why depleted peridotites overlie more fertile peridotites and how deep regions of the mantle are able to remain fertile over geologic time

search for extractable fullerenes in clays from the cretaceous tertiary boundary of the woodside creek and flaxbourne river sites new zealand abstract when fullerenes were first discovered to form spontaneously in condensing carbon vapors kroto et al 1985 it was suggested that they might be widely distributed in the universe searches for fullerenes in meteorites see devries et al 1993 were unsuccessful but c 60 and c 70 were reported to occur on earth in samples of shungite a meta anthracite from a deposit near shunga russia buseck et al 1992 and in fulgurite a substance formed when lightning strikes certain soils or rocks daly et al 1993 the occurrence of fullerenes in shungite is particularly surprising since fullerene synthesis in the laboratory has always involved gas phase chemistry at temperatures over 1000 c such conditions may be attained during lightning strikes but shungite is believed to have formed from carbonaceous material creeping into fissures of a precambrian rock which metamorphosed under extreme pressures if the original carbonaceous material did not already contain fullerenes perhaps from wildfires they must have formed during the metamorphism by as yet unknown solid or liquid phase mechanisms

temperature distribution in the crust and mantle in an attempt to understand the temperature distribution in the earth experimental constraints on the geotherm in the crust and mantle are considered the basic form of the geotherm is interpreted on the basis of two dominant mechanisms by which heat is transported in the earth 1 conduction through the rock and 2 advection by thermal flow data reveal that 1 the temperature distributions through continental lithosphere and through oceanic lithosphere more than 60 million years old are practically indistinguishable 2 crustal uplift is instrumental in modifying continental geotherms and 3 the average temperature through the archean crust and mantle was similar to that at present it is noted that current limitations in understanding the constitution of the lower mantle can lead to significant uncertainties in the thermal response time of the planetary interior

permian triassic boundary in the central transantarctic mountains antarctica the permian triassic boundary occurs within a relatively complete terrestrial sequence in the shackleton glacier area of the central transantarctic mountains the boundary is within a 7 to 10 m thick interval between the permian glossopteris flora and the lower triassic lystrosaurus fauna this interval representing on the order of 200 k y records some of the events that occurred in the transition from the permian to triassic in the best documented section at graphite peak in the beardmore glacier region protohaploxypinus microcorpus zone palynomorphs which we assign to the latest permian record the declining glossopteris flora and occur near the top of the buckley coal measures just below a previously reported major negative 13c excursion in the shackleton glacier area the permian glossopteris flora including fossil wood roots and leaves occurs within the lower part of the fremouw formation the antarctic lystrosaurus assemblage of early triassic age has several species in common with the south african fauna that lived 20 to 35 closer to the equator the migration of vertebrates from southern africa into antarctica in the early triassic supports hypotheses of runaway greenhouse warming possibly related to co2 emissions from siberian flood basalts and large methane gas releases changes in flora bracketing the first of the major negative 13c anomalies near the boundary in antarctica and in east greenland support the hypothesis that a global event perhaps through mutations caused by enhanced ultraviolet radiation may have played a role in the destruction of floras

testing for fullerenes in geologic materials oklo carbonaceous substances karelian shungites sudbury black tuff fullerenes have been reported from diverse geologic environments since their discovery in shungite from karelian russia our investigation is prompted by the presence of onionskin like structures in some carbonaceous substances associated with the fossil nuclear fission reactors of oklo gabon the same series of extractions and the same instrumental techniques laser desorption ionization and high resolution mass spectroscopy electron impact mass spectroscopy were employed to test for fullerenes in samples from three different localities two sites containing putative fullerenes sudbury basin and russian karelia and one new location oklo gabon we confirm the presence of fullerenes c 6 0 and c 7 0 in the black tuff of the onaping formation impact breccia in the sudbury basin but we find no evidence of fullerenes in shungite samples from various locations in russian karelia analysis of carbonaceous substances associated with the natural nuclear fission reactors of oklo yields no definitive signals for fullerenes if fullerenes were produced during sustained nuclear fission at oklo then they are present below the detection limit 100 fmol or they have destabilized since formation contrary to some expectations geologic occurrences of fullerenes are not commonplace

a search for anomalies in the lowermost mantle using seismic bulletins abstract for deep events and epicentral distances around 75 the bulletins of the international seismological centre bisc contain many secondary arrivals between p and pcp the reflection from the core mantle boundary cmb which cannot be explained by current spherical symmetric earth models assuming that these arrivals in the p coda are reflections from p velocity anomalies in the lower mantle we calculate the associated reflection points geographical coordinates and distance from the cmb and map both strength relative density of reflection points in bins in the lower mantle and distance of the reflectors from the cmb on a global scale the regions with these anomalous bins cover 3 of the 50 of the lowermost mantle that can be analysed with this data set the most significant regions with anomalous bins values in parentheses give a preliminary estimate of the distance of the reflector from the cmb are under the north atlantic ridge 250 km northern central siberia 230 km japan 180 km the central mid atlantic ridge 310 and 260 km and off the coast of ecuador 340 km the presence of reflectors in one of these regions has already been confirmed by detailed seismic studies using waveform data from arrays and networks a slight 2 3 p velocity contrast is sufficient to produce measurable reflection amplitudes in the distance range of 70 80 ten percent of the lower mantle sampled by this study is covered by bins with no or very few secondary arrivals in the p coda the most significant regions with such a normal lower mantle are under central america the caroline and marshall islands in the eastern pacific the area of hawaii and the easter islands and the northern atlantic identification of the regions with anomalous bins serves to locate the areas of the lowermost mantle which should be analysed further by using the full information content of seismograms the study of the travel time the amplitude and the form of the wavefield recorded preferably at seismic arrays dense networks will allow the determination of the anomalous velocity structure of the core mantle transition zone in more detail the most promising areas for such a study are given here but further anomalies are likely to exist

an extraterrestrial impact at the permian triassic boundary becker et al 1 presented geochemical evidence that suggests that the largest mass extinction in earth history at the permian triassic boundary ptb 250 million years ago ma coincided with an extraterrestrial impact comparable in size to the one that likely caused the end cretaceous extinctions 65 ma 2 although becker et al analyzed material from sections in hungary japan and china the hungarian section yielded no extraterrestrial signature and their identification of the ptb in the japanese section is questioned in the accompanying comment by isozaki below thus only their analyses of the chinese section provide hitherto uncontested evidence for an impact at the boundary in the form of data on the abundance and composition of fullerenes in the boundary clay a volcanic ash layer called bed 25 at meishan china 3 although fullerenes may be purely terrestrial see e g 4 becker et al report that the fullerenes from the meishan ash carry extraterrestrial noble gases in the cage structure rich in 3 he and with distinctive 3 he 36 ar and 40 ar 36 ar ratios and that this signature therefore derived from a bolide impact here we report that we are able to detect fullerene hosted extraterrestrial 3 he neither in aliquots of the same meishan material analyzed by beckeret al nor any in samples of a second chinese ptb section and that we thus find no evidence for an impact

characteristics of claystones across the terrestrial permian triassic boundary evidence from the chahe section western guizhou south china abstract x ray diffraction xrd scanning electronic microscopy sem and x ray fluorescence spectroscopy xfs studies were undertaken for claystones and or mudstones from the chahe section a terrestrial permian triassic boundary tptb section our results indicate that the compositions of claystones in the permian triassic boundary ptb interval beds 66f 68 outlined by biostratigraphy are different from claystones and or mudstones found either below or above the interval of the same section the clay minerals in the claystones of the ptb interval are mainly composed of illite montmorillonite interlayers with a few montmorillonites and chlorites the other claystones and or mudstones underlying and overlying the ptb consist of chlorites and or kaolinites some authigenic clastic minerals such as hexagonal dipyramid quartz and zircons are only found in claystones in the ptb interval from the chahe section and some marine ptb sections in western guizhou and eastern yunnan southwestern china in addition some elements are present in abnormal concentrations in the claystones of the ptb interval as well most important is that we found no spherules in all the claystones studied indicating no evidence of an extraterrestrial impact during the permian triassic transition the particular characteristics of the tptb claystones at the chahe section indicate their volcanic origin and thus provide a reliable auxiliary event marker for high resolution demarcation of the tptb in south china they are also indicative in the marine ptb claystones in south china thus the ptb claystones can be used as auxiliary markers for high resolution correlation of the ptb from marine facies to land in south china when direct fossil evidence in the ptb sequence is lacking

chemical stratification in the silicate earth abstract the largest density contrast between magmas and common ferromagnesian minerals in the mantle occurs at two locations these are nearest the earth s surface and at about 650 700 km depth where the lower mantle mineral assemblage becomes stable at solidus temperatures the large density contrast between magmas and olivine nearest the surface diminishes to zero somewhere between the middle and lower stratigraphic sections of the upper mantle it is also here where the composition of all anhydrous magmas is most similar to that of an undepleted garnet iherzolite composition for an earth that has differentiated by fractional crystallization and melting processes which depend on the separation of crystalline phases from silicate liquids having different densities the 650 km discontinuity could represent a chemical boundary layer the chemical change in the early archean could have been from primordial upper mantle compositions above the boundary layer to differentiated lower mantle compositions below a primary stratigraphic model is offered for the distribution of depleted enriched and primordial isotopic mantle components formed by the transport fate of magmas in the beginning of earth history depleted morb source regions were established in the uppermost part of the upper mantle primordial mantle was located at the middle to the deepest regions of an upper mantle which was processed by anhydrous melting and crystallization enriched and depleted components could have been formed at these levels also by igneous processing in the presence of h 2 o or co 2 and involving highly compressible magmas the lower mantle became heterogeneous with enrichments at the top and depletions elsewhere it is suggested that the present day isotopic structure of the mantle has inherited elements of this primary stratification primordial 143 nd 144 nd and 87 sr 86 sr observed in oceanic islands basalts are located in the middle of upper mantle convection cells enriched ratios found in both oceanic islands basalt and kimberlite could have originated near and on either side of the 650 km chemical boundary layer

melting temperature distribution and fractionation in the lower mantle abstract the melting curve of perovskite mgsio3 and the liquidus and solidus curves of the lower mantle were estimated from thermodynamic data and the results of experiments on phase changes and melting in silicates the initial slope of the melting curve of perovskite mgsio3 was obtained as d t m d p 77 k gpa 1 at 23 gpa the melting curve of perovskite was expressed by the kraut kennedy equation as t m k 917 1 29 6 v v 0 where tm 2900 k and p 23 gpa and by the simon equation p gpa 23 21 2 t m k 2900 1 75 1 the liquidus curve of the lower mantle was estimated as t liq 0 9 t m perovskite and this gives the liquidus temperature tliq 7000 500 k at the mantle core boundary the solidus curve of the lower mantle was also estimated by extrapolating the solidus curve of dry peridotite using the slope of the solidus curve of magnesiowustite at high pressures the solidus temperature is 5000 k at the base of the lower mantle if the temperature distribution of the mantle was 1 5 times higher than that given by the present geotherm in the early stage of the earth s history partial melting would have proceeded into the deep interior of the lower mantle estimation of the density of melts in the mgo feo sio2 system for lower mantle conditions indicates that the initial melt formed by partial fusion of the lower mantle would be denser than the residual solid because of high concentration of iron into the melt thus the melt generated in the lower mantle would tend to move downward toward the mantle core boundary this downward transportation of the melt in the lower mantle might have affected the chemistry of the lower mantle such as in the d layer and the distribution of the radioactive elements between mantle and core

high pressure equation of state of molten anorthite and diopside new hugoniot equation of state data for molten diopside at 1773 k and molten anorthite at 1923 k are reported to 38 and 35 gpa respectively the diopside data initial density 2 61 mg m 3 are described by a straight line fit to the shock velocity particle velocity results of u s 3 30 1 44 u p km s 1 and our preferred fit to the anorthite data initial density 2 55 mg m 3 is given by u s 2 68 1 42 u p km s 1 reduction of the data to a third order birch murnaghan isentrope assuming the gruneisen ratio times the density is a constant and the mie gruneisen equation of state gives k 0s 22 4 gpa and k s 6 9 for diopside for anorthite we calculate k 0s 17 9 gpa and k s 5 3 the present data for diopside are used to calculate the diopside solidus at high pressures we expect the solidus to be shallow above 10 gpa but the lack of data on the variation of either the gruneisen parameters of the liquid and crystal or the heat capacity and thermal expansion at elevated pressures makes extrapolation of fusion curves uncertain solidus temperatures of 2400 2500 k and 2560 2705 k for diopside are calculated at 10 and 20 gpa respectively the new data are combined with those of rigden et al 1988 for the di 0 64 a 0 36 eutectic composition to examine the degree to which such liquids mix ideally with respect to volume up to 25 gpa for the eutectic composition at 1400 c we calculate the volumes of the an and di mix nearly ideally to 25 gpa we find that the ratio of the partial molar volumes of the oxides in silicate melts to that of the crystal oxides at 1673 k and 1 atm is 1 0 0 1 for a wide range of oxide components for the low pressure tetrahedrally coordinated oxides e g sio 2 al 2o 3 fe 2o 3 the ratio is 1 3 with respect to oxides such as stishovite corundum and hematite in which the cations are octahedrally coordinated by oxygens if changes in coordination of al and si from tetrahedral at low pressures to octahedral at high pressures occur in melts they do so gradually over an interval of 40 gpa although 1 atm bulk moduli for a wide compositional range of silicate melts are similar the differences in integrated compression to mixed oxide like high pressure configurations are reflected mainly by variations in k t k t is found to vary inversely with fraction of network forming initially tetrahedrally coordinated cations e g al 3 si 4 thus k t which may be uncertain by 1 5 is estimated to vary from 7 for molten anorthite enstatite and diopside to 8 for molten ferrosilite to 10 for molten forsterite and to 11 for molten fayalite

characterization of organic matter associated with uranium deposits in the francevillian formation of gabon lower proterozoic abstract elemental analysis organic petrography and high resolution transmission electron microscopy were used to study organic matter in lower proterozoic rocks of the francevillian series in africa results show a convincing relationship between solid bitumens derived from thermal alteration of crude oil and deposition of uraninite ores evidence is presented that suggests the presence of migration paths for crude oil in associated sandstones moreover the solid bitumens appear to have been further altered by radiation damage as a consequence of oxidation and uranium mineralization

the importance of being cratered the new role of meteorite impact as a normal geological process this paper is a personal and in many ways incomplete view of the past development of impact geology and of the newly recognized importance of impact events in terrestrial geological history it also identifies some exciting scientific challenges for future investigators to determine the full range of impact effects preserved on the earth to apply the knowledge obtained from impact phenomena to more general geological problems and to continue the merger of the once exotic field of impact geology with mainstream geosciences since the recognition of an impact event at the cretaceous tertiary k t boundary much current activity in impact geology has been promoted by traditionally trained geoscientists who have unexpectedly encountered impact effects in the course of their work their studies have involved 1 the recognition of additional major impact effects in the geological record the chesapeake bay crater the alamo breccia and multiple layers of impact spherules in precambrian rocks and 2 the use of impact structures as laboratories to study general geological processes e g igneous petrogenesis at sudbury canada and archean crustal evolution at vredefort south africa other research areas in which impact studies could contribute to major geoscience problems in the future include 1 comparative studies between low level 7 gpa shock deformation of quartz and the production of quartz cleavage in both impact and tectonic environments and 2 the nature origin and significance of bulk organic carbon kerogen and other carbon species in some impact structures gardnos norway and sudbury canada

further evidence for the lay discontinuity beneath northern siberia and the north atlantic from short period p waves recorded in france abstract we analyze data from the french laboratoire de detection geophysique ldg network of digital short period seismic stations the p waves from several earthquakes in the kuril okhotsk region display clear secondary arrivals in the 75 85 range which are not explained by smooth lower mantle models the move out of the arrivals across the network indicates a deep mantle origin we interpret them as waves reflected off or transmitted at the lay discontinuity about 300 km above the core mantle boundary the bounce points at this discontinuity are located beneath northern siberia slightly to the northwest of the region for which a similar structure has been reported we propose tools for investigating the lateral variations of the d structure on the scale 100 1000 km the method we propose is based on the deconvolution of the data or convolution of synthetics by a source time function derived from the data we show that the method helps identification of the waves that interact with the lay discontinuity and enables a more objective mapping of its lateral variations evidence for bumps a few kilometers high on the lateral scale of a few tens of kilometers is proposed we also probe a spot of the lower mantle beneath the north atlantic a detailed analysis of the waveforms from a chiapas earthquake suggests that the lay discontinuity is also present in that part of the world

compression of tetrahedrally bonded sio2 liquid and silicate liquid crystal density inversion we have investigated the response to pressure of liquid sio2 by performing a quantitatively realistic monte carlo simulation the model liquid was restricted to at most four fold si o coordination by the effective imposition of an infinite potential barrier to a fifth bond we thus obtained an unambiguous comparison of the compression mechanisms of solid and liquid tetrahedral networks in spite of this restriction the density of the simulated liquid exceeds that of the corresponding models of quartz coesite and cristobalite at high pressure the efficient compression of the liquid results from a continuous restructuring of the network that leaves the mean si si distance virtually unchanged and does not require an increase in the coordination number the restructuring is effected by local breaking and reconnecting of bonds a mechanism that is not available to a perfect crystal

dynamics of double subduction numerical modeling abstract double subduction is a geodynamic process in which two plates following each other are synchronously subducted double subductions are known for both modern izu bonin marianas and ryukyu arcs and ancient west himalaya collision zone plate tectonics however our knowledge about this process is limited to conceptual schemes and some restricted analogue experiments in order to fill this gap we performed 2d numerical experiments using a coupled petrological thermomechanical approach based on finite differences and marker in cell techniques combined with thermodynamic database for the mantle we investigated the influence of convergence rate intermediate plate length activation volume of the mantle dislocation creep and age of the lithosphere based on these experiments we conclude that a subduction rates at two zones running in parallel differ and vary in time even when the total convergence rate remains constant supremacy of either subduction zone depends on physical parameters such as i relative rates of the plates ii slab ages and iii length of the middle plate b subduction dynamics of the double subduction system involves several processes unknown in simple subduction systems such as i eduction i e un subduction ii subduction re initiation iii subduction flip triggered by shallow slab breakoff and iv turn over of detached slabs to up side down attitudes c simulated tomographic structures related to slab propagation account for both penetration and non penetration of the 660 km discontinuity non penetration is favored by i low convergence rate ii faster relative movement of the overriding plate iii young age of the subducting slab and iv up side down turn over of detached slab

carbon isotope excursions and microfacies changes in marine permian triassic boundary sections in hungary abstract several permian triassic boundary sections occur in various structural units within hungary these sections represent different facies zones of the western palaeotethys margin the gardony core in the ne part of the transdanubian range typically represents the inner ramp while the balvany section in the bukk mountains of northern hungary represents an outer ramp setting the two sections have different patterns for their 13 c values the balvany section shows a continuous change towards more negative 13 c values starting at the first biotic decline followed by a sharp quasi symmetric negative peak at the second decline the appearance of the 13 c peak has no relationship to the lithology and occurs within a shale with low overall carbonate content indicating that the peak is not related to diagenesis or other secondary influences instead the shift and the peak reflect primary processes related to changes in environmental conditions the continuous shift in 13 c values is most probably related to a decrease in bioproductivity whereas the sharp peak can be attributed to an addition of c strongly depleted in 13 c to the ocean atmosphere system the most plausible model is a massive release of methane hydrate the quasi symmetric pattern suggests a rapid warming cooling cycle or physical unroofing of sediments through slope failure and releasing methane hydrate the gardony 1 core shows a continuous negative 13 c shift starting below the p t boundary however the detailed analyses revealed a sharp 13 c peak in the boundary interval just below the major biotic decline although its magnitude doesn t reach that observed in the balvany section based on careful textural examination and high resolution stable isotope microanalyses we suggest that the suppression of the 13 c peak that is common in the oolitic boundary sections is due to combined effects of condensed sedimentation sediment reworking and erosion as well as perhaps diagenesis

precambrian vein pyrobitumen evidence for petroleum generation and migration 2 ga ago abstract isotopic optical reflectance and chemical analyses of large pure samples of lower proterozoic vein pyrobitumens anthraxolite and thucholite of older reports collected from five widely separated localities in the great lakes region of the united states and canada suggest that in the lower proterozoic oil was generated from kerogen and migrated in much the same way as during the phanerozoic furthermore maturation and organic metamorphism followed the same successive stages that mark the generation and destruction of phanerozoic petroleum kerogens derived from algae and bacteria were deposited with subaqueous muds that ultimately became black shales or slates some of the kerogen however yielded petroleum which migrated into fractures and subsequently became pyrobitumen the 13c values average 32 6 pdb this value compares favorably with those from phanerozoic petroleum and asphaltites and is consistent with the proposition that the carbon isotopes were fractionated by biological activity reflectance values of the pyrobitumens range from 0 9 for elliot lake ontario to 9 5 for iron river michigan and h c ratios range from 0 6 for elliot lake to 0 1 for sudbury ontario when compared with the stages of petroleum maturation these values indicate maturation which ranges from the catagenesis stage through the metagenesis stage of petroleum generation and metamorphism

computation of seismic profiles from mineral physics the importance of the non olivine components for explaining the 660 km depth discontinuity the recent increasing number of experimental works leads us to review the elastic properties and mineralogical transformations of mantle minerals the updated data set is used to compute seismic profiles for two petrological models along three adiabatic temperature profiles these profiles are chosen to stress out the influence of non olivine minerals on seismic parameters and to represent cold and horizontally averaged temperature profiles of the earth s mantle in a first part starting compositions of pyrolite and piclogite and a single layer convection are assumed the results clearly point out the importance of the non olivine part of the mineralogy two scenarios are found to explain the 660 km depth discontinuity

static compression and olivine flotation in ultrabasic silicate liquid piston cylinder techniques have been used to observe static compressions of ultrabasic silicate liquids to 6 gpa and 2000 c compressions are measured by bracketing sinking and floating of olivine crystals of known density at run conditions komatiite peridotite and their liquid mixtures with fe2sio4 all show constant density changes with pressure of 0 07 g cm3 gpa along their liquidi these results confirm shock wave studies and ultrasonic studies which show weak compositional effects on compressibility of basic to ultrabasic silicate liquid the techniques converge in supporting the conjecture of stolper et al 1981 that ultrabasic silicate liquids may be denser than their equilibrium coexisting olivines and pyroxenes at high compressions the pressure of this density inversion is 7 8 gpa for the compositions studied olivine flotation provides an important constraint upon earth evolution models that include extensive melting during early differentiation it also provides a mechanism for concentrating high mg si olivine in the upper mantle without unduly perturbing other geochemical parameters a full evaluation of the physical and geochemical consequences is required at an early date