collisional history of h chondrites the cosmic ray exposure histories of ordinary chondrites were recently reviewed marti and graf 1992 here we discuss in detail currently available cosmic ray exposure records and the adopted exposure ages of individual h chondrites we further present analyses of the distinct histograms of petrographic subgroups and the implications for orbital evolution and collisional records in addition to the stochastic events 7 to 8 m y ago a peak at 33 ma represents a statistically significant deviation from an exponential age distribution and signals a major collisional event at this time the h6 subgroup also recorded a similar event 24 m y ago these records present significant arguments against a continuous supply of h chondrites from the asteroid belt we show that the records of fall times for h5s are distinct from other subgroups and that a different orbit for the h5 parent is indicated in collisional events 7 to 8 m y ago the systematics of noble gas losses in the h5 subgroup are consistent with this interpretation the evidence for stochastic fragmentation and subsequent delivery to earth of h chondrites suggests that their present predominance among falls may represent a deviation from a representative population distribution

the stubenberg meteorite an ll6 chondrite fragmental breccia recovered soon after precise prediction of the strewn field on march 6 2016 at 21 36 51 ut extended areas of upper austria bavaria germany and the southwestern part of the czech republic were illuminated by a very bright bolide this bolide was recorded by instruments in the czech part of the european fireball network and it enabled complex and precise description of this event including prediction of the impact area so far six meteorites totaling 1473 g have been found in the predicted area the first pieces were recovered on march 12 2016 on a field close to the village of stubenberg bavaria stubenberg is a weakly shocked s3 fragmental breccia consisting of abundant highly recrystallized rock fragments embedded in a clastic matrix the texture the large grain size of plagioclase and the homogeneous compositions of olivine fa31 4 and pyroxene fs25 4 clearly indicate that stubenberg is an ll6 chondrite breccia this is consistent with the data on o ti and cr isotopes stubenberg does not contain solar wind implanted noble gases data on the bulk chemistry ir spectroscopy cosmogenic nuclides and organic components also indicate similarities to other metamorphosed ll chondrites noble gas studies reveal that the meteorite has a cosmic ray exposure cre age of 36 3 ma and that most of the cosmogenic gases were produced in a meteoroid with a radius of at least 35 cm this is larger than the size of the meteoroid which entered the earth s atmosphere which is constrained to 20 cm from short lived radionuclide data in combination this might suggest a complex exposure history for stubenberg

global upper mantle structure from finite frequency surface wave tomography 1 we report global shear wave velocity structure and radial anisotropy in the upper mantle obtained using finite frequency surface wave tomography based upon complete three dimensional born sensitivity kernels because wavefront healing effects are properly taken into account finite frequency surface wave tomography improves the resolution of small scale mantle heterogeneities especially for deep anomalies that are constrained by the longest period surface waves in our finite frequency model ffsw1 the globally averaged radial anisotropy shows a transition from positive sh sv to negative anisotropy sv sh at about 220 km consistent with a change in the dominant mantle circulation pattern from predominantly horizontal flow at shallow depths to vertical flow at greater depths the radial anisotropy beneath cratons and the old pacific plate agrees well with previous studies however our model exhibits a strong negative radial anisotropy at depths greater than 120 km beneath mid ocean ridges a feature that is not present in previous upper mantle models more interestingly the depth extent of the ridge anomalies is distinctly different beneath fast and slow spreading centers anomalies beneath fast spreading centers are stronger but the strength decreases rapidly below 250 km in contrast beneath slow spreading centers such as the northern mid atlantic ridge and the red sea anomalies extend down at least to the top of the transition zone the different depth extent of the ridge anomalies suggests that the primary driving force of slow spreading seafloor may be different from that of fast spreading seafloor and that active upwelling beneath slow spreading ridges may play a major role in the opening of the seafloor

burial history and diagenetic reaction kinetics relations among burial histories deduced from stratigraphy thermal regimes imposed by tectonics and sedimentation and rates of diagenetic reactions extrapolated from experimental data have been explored by using sedimentation diagrams plots of burial with respect to the sediment water or sediment air interface as a function of time elapsed since deposition one can estimate paleogeotherms from such plots using assumptions on heat flow thermal conductivities compaction and cementation effects on porosity and convecting formation water systems from these one can deduce the temperature history of a sediment as a function of postdepositional time that history can be converted to the integrated value of temperature as a function of time this value which takes into ccount the total contribution of time and temperature is the relevant parameter for reaction kinetics a plot of the time temperature integral versus postdepositional time for a given formation can then be compared with the time temperature integral for specific yields of a diagenetic reaction to deduce at what stage in its history a sediment would have accumulated sufficient time and thermal energy to accomplish a given extent of reaction these deductions can be compared with petrologic information on the time of origin of diagenetic phases

mantle flow in regions of complex tectonics insights from indonesia 1 indonesia is arguably one of the tectonically most complex regions on earth today due to its location at the junction of several major tectonic plates and its long history of collision and accretion it is thus an ideal location to study the interaction between subducting plates and mantle convection seismic anisotropy can serve as a diagnostic tool for identifying various subsurface deformational processes such as mantle flow for example here we present novel shear wave splitting results across the indonesian region using three different shear phases local s sks and downgoing s to improve spatial resolution of anisotropic fabrics allows us to distinguish several deformational features for example the block rotation history of borneo is reflected in coast parallel fast directions which we attribute to fossil anisotropy furthermore we are able to unravel the mantle flow pattern in the sulawesi and banda region we detect toroidal flow around the celebes sea slab oblique corner flow in the banda wedge and sub slab mantle flow around the arcuate banda slab we present evidence for deep sub 520 km anisotropy at the java subduction zone in the sumatran backarc we measure trench perpendicular fast orientations which we assume to be due to mantle flow beneath the overriding eurasian plate these observations will allow to test ideas of for example slab mantle coupling in subduction regions

a comparison of khuff and arab reservoir potential throughout the middle east a compilation of average porosity and permeability data for petroleum reservoirs in the permian triassic khuff formation and the jurassic arab formation shows that most khuff reservoirs have an average porosity of less than 12 whereas most arab reservoirs have an average porosity of 12 26 higher porosity correlates with shallower depth suggesting that burial diagenesis is the main cause of the overall porosity difference between these units deeper burial of khuff reservoirs is inferred to have resulted in greater porosity loss by chemical compaction and associated cementation a broad correlation also exists between average porosity and average permeability suggesting that deeper burial and the resulting porosity decrease are also a primary cause of the lower permeabilities of the khuff reservoirs in addition to greater burial depth however a combination of depositional and early diagenetic factors is also reflected in the lower average porosity and permeability values of the khuff reservoirs khuff strata were deposited on an extensive poorly circulated very low relief shelf and consist in large part of interbedded mudstones and grainstones having relatively fine grain size with major amounts of depositional calcium sulfate present arab reservoirs were deposited under better circulated conditions near platform margins facing deep intracratonic basins and thus have coarser more grain dominated fabrics and lesser overall content of chemically precipitated grains calcium sulfate and dolomite khuff deposits were likely composed of less stable mineralogy than arab sediments because the late permian was a time of aragonite seas whereas the late jurassic was a time of calcite seas the combined result of these factors is that arab reservoirs are characterized by greater preservation of primary depositional pore types more coarsely crystalline dolomite fabrics and lesser plugging by anhydrite finally a possible factor affecting the average porosity and permeability values is petroleum composition which is gas in most khuff reservoirs and oil in arab reservoirs lower economic cutoff values for gas production would favor inclusion of low permeability zones in khuff reservoirs thus reducing average reservoir values two main aspects of these results are innovative this is the first time that porosity and permeability values for either khuff or arab reservoirs have been examined regionally second the conclusion that thermal exposure is the primary control on average porosity and permeability in these units is consistent with previous work from other carbonates but is new for the middle east

noble gases in h chondrites and potential differences between antarctic and non antarctic meteorites abstract thirty one antarctic h chondrites from the allan hills have been analyzed for their noble gases seven of the specimens contain solar gases thirteen have a cosmic ray exposure age around 8 ma both fractions are as observed for h chondrites from the rest of the world scrutiny of the data for paired samples yields a minimum number of 17 independent falls with 6 falls required for the 8 ma peak of exposure age the distribution of exposure ages as well as that of radiogenic 4 he and 40 ar yield no evidence that h chondrites from the allan hills region represent a mixture of populations that is different from that brought to moderate latitudes of the earth in more recent times

sandstone porosity as a function of thermal maturity sandstone porosity decreases in the subsurface as a power function of thermal maturity phi a m sup b where phi is porosity and m is a measure of thermal maturity representing integrated time temperature history a and b are constants for a given sandstone of homogeneous properties but vary between data sets the commonly observed exponential dependence of sandstone porosity upon depth follows as a special case from this power function relation when temperature increases linearly with depth the consideration of sandstone porosity in terms of time temperature exposure offers advantages in the comparison of porosity data from diverse geologic settings the recognition of unusual porosity within a sandstone sequence and the prediction of porosity ahead of the drill and at times in the geologic past

pressure effect on forsterite dislocation slip systems implications for upper mantle lpo and low viscosity zone abstract in order to better constrained the effect of pressure p on olivine dislocation slip system activities deformation experiments were carried out in a deformation dia apparatus d dia on pure forsterite fo100 single crystals at p 5 7 gpa temperature t 1675 k differential stress and specimen strain rates e were monitored in situ by synchrotron x ray diffraction and radiography respectively two compression directions were tested promoting either 1 0 0 slip or 0 0 1 slip in 0 1 0 crystallographic plane comparison of the obtained high p rheological data with room p data previously reported by darot and gueguen 1981 shows that 1 0 0 slip is strongly inhibited by pressure while 0 0 1 slip is virtually p insensitive this translates in creep power laws into a high activation volume v a 15 3 cm 3 mol for 1 0 0 0 1 0 slip system and v c 0 1 2 cm 3 mol for 0 0 1 0 1 0 slip system using these laws along geotherms at natural condition shows that the 1 0 0 slip 0 0 1 slip transition may occur at 200 km depth in the upper mantle and be responsible for the observed lattice preferred orientation lpo transition a rheological law for polycrystalline forsterite is deduced from the single crystal rheological laws assuming that individual grains are randomly oriented in the aggregate applying the aggregate law within a 2d geodynamic model of upper mantle couette flow suggests that the pressure dependence of olivine dislocation slip activities may partly explain the low viscosity zone lvz observed underneath oceanic plates

mechanical and chemical compaction in fine grained shallow water limestones abstract artificial compaction of in situ cores of modern sediments from differing sedimentary environments resulted in 1 reduction of sediment thickness by 50 percent and more 2 reduction of initial porosities of 65 to 75 percent to 35 to 45 percent 3 creation of megascopic textures almost identical to many ancient lime mud and wackestones 4 creation of organic wispy stylolite like layers that in nature probably would initiate dissolution and stylolite development given burial and time 5 chemical compaction evidenced by thin sections showing quartz grains piercing mollusc shells without causing fractures and sem evidence of solutional interfitting of 1 to 4 m size aragonitic carbonate grains 6 obliteration of pellets and birdseye or fenestral voids in those sediments here early cementation was lacking pellets were preserved in slightly cemented bahama bank muds compacted to half the original thickness 7 obliteration of identifiable marine grasses and vertical root tube voids 8 mashing of sediment filled circular burrows to produce ellipsoidal structures significant mechanical compaction resulted from pressures simulating less than 1 000 ft 305 m of burial increasing loads to an equivalent of more than 10 000 ft 3 400 m did not significantly increase compaction or reduce sediment core length chemical compaction pressure dissolution was detected only in sediment cores compacted to pressures greater than 10 000 ft 3 400 m of burial these short term experiments suggest that chemical compaction would begin at much shallower depths given geologic time compaction experiments that caused chemical compaction lend support to the well established hypothesis that cement required to produce a low porosity low permeability fine grained limestone is derived internally dissolution ion diffusion and reprecipitation are considered the m st likely processes for creating significant thicknesses of dense limestones in the geologic record continuation of chemical compaction after significant porosity reduction necessitates expulsion of connate fluids possibly including hydrocarbons

the l3 6 chondritic regolith breccia northwest africa nwa 869 ii noble gases and cosmogenic radionuclides abstract we measured cosmogenic radionuclides and noble gases in the l3 6 chondrite breccia northwest africa nwa 869 one of the largest meteorite finds from the sahara concentrations of 10be 26al and 36cl in stone and metal fractions of six fragments of nwa 869 indicate a preatmospheric radius of 2 0 2 5 m the 14c and 10be concentrations in three fragments yield a terrestrial age of 4 4 0 7 kyr whereas two fragments show evidence for a recent change in shielding most likely due to a recent impact on the nwa meteoroid approximately 105 yr ago that excavated material up to approximately 80 cm deep and exposed previously shielded material to higher cosmic ray fluxes this scenario is supported by the low cosmogenic 3he 21ne ratios in these two samples indicating recent loss of cosmogenic 3he most nwa samples except for clasts of petrologic type 4 6 contain significant amounts of solar ne and ar but are virtually free of solar helium judging from the trapped 4he 20ne ratio of approximately 7 trapped planetary type kr and xe are most clearly present in the bulk and matrix samples where abundances of 129xe from decay of now extinct 129i are highest cosmogenic 21ne varies between 0 55 and 1 92 10 8 cm3 stp g 1 with no apparent relationship between cosmogenic and solar ne contents low cosmogenic 22ne 21ne c ratios in solar gas free specimens are consistent with irradiation in a large body combined 10be and 21ne concentrations indicate that nwa 869 had a 4 cosmic ray exposure cre age of 5 1 myr whereas elevated 21ne concentrations in several clasts and bulk samples indicate a previous cre of 10 30 myr on the parent body most probably as individual components in a regolith unlike many other large chondrites nwa 869 does not show clear evidence of cre as a large boulder near the surface of its parent body radiogenic 4he concentrations in most nwa 869 samples indicate a major outgassing event approximately 2 8 gyr ago that may have also resulted in loss of solar helium

itqiy a study of noble gases and oxygen isotopes including its terrestrial age and a comparison with zaklodzie we report noble gas oxygen isotope 14c and 10be data of itqiy as well as noble gas 14c and 10be results for zaklodzie both samples have been recently classified as anomalous enstatite meteorites and have been compared in terms of their mineralogy and chemical composition the composition of enstatite and kamacite and the occurrence of specific sulfide phases in itqiy indicate it formed under similar reducing conditions to those postulated for enstatite chondrites the new results now seem to point at a direct spatial link the noble gas record of itqiy exhibits the presence of a trapped subsolar component which is diagnostic for petrologic types 4 6 among enstatite chondrites the concentration of radiogenic 4he is very low in itqiy and indicates a recent thermal event its 21ne cosmic ray exposure age is 30 1 3 0 ma and matches the most common age range of enstatite chondrites mostly el6 chondrites but not that of zaklodzie itqiy s isotopic composition of oxygen is in good agreement with that observed in zaklodzie as well as those found in enstatite meteorites suggesting an origin from a common oxygen pool the noble gas results on the other hand give reason to believe that the origin and evolution of itqiy and zaklodzie are not directly connected itqiy s terrestrial age of 5800 500 years sheds crucial light on the uncertain circumstances of its recovery and proves that itqiy is not a modern fall whereas the 14c results from zaklodzie suggest it hit earth only recently

forsterite to wadsleyite phase transformation under shear stress and consequences for the earth s mantle transition zone we have studied the phase transformation of forsterite to wadsleyite under shear stress at the earth s transition zone pressure and temperature conditions two step experiments were performed using a multi anvil press first we hot pressed iron free forsterite at 6 or 11 gpa and 1100 c then we deformed a slab of this starting material using a direct simple shear assembly at 16 gpa and 1400 c for 1 15 35 40 or 60 min both the starting material and the deformed samples were characterized using optical and scanning electron microscopy including measurements of crystal preferred orientations cpo by electron back scattered diffraction ebsd transmission electron microscopy tem and fourier transform infrared spectroscopy ftir the phase transformation occurs very rapidly in less than 1 min and metastable forsterite relics are not observed after deformation the grain size of wadsleyite is slightly smaller than the forsterite starting material the water contents obtained from ftir analyses in forsterite and wadsleyite are 65 124 wt ppm h2o and 114 736 wt ppm h2o respectively which are well below water solubility at similar conditions in the presence of free water wadsleyite aggregates display weak cpo patterns with 1 0 0 axes concentrated at low angle to the shear direction 0 1 0 axes perpendicular to the shear plane and nearly random 0 0 1 axes only a few dislocations were observed in wadsleyite with tem this observation is consistent with the assumption that most dislocations formed during the initial high stress stages of these stress relaxation experiments were consumed in the phase transformation probably enhancing the transformation rate cpo patterns vary as a function of the water content with increasing water content the density of 1 0 0 axes parallel to the shear direction decreases and the density of 0 0 1 axes increases viscoplastic self consistent modeling of cpo evolution using previously reported glide systems for wadsleyite i e 1 0 0 0 k l and 1 2 111 101 cannot reproduce the measured cpo unless the 0 0 1 0 1 0 system for which dislocations have not been observed by tem is also activated in addition wadsleyite grain growth suggests the participation of diffusion assisted processes in deformation calculated anisotropies for p and s waves using measured cpo are always below 1 this very low anisotropy is due to both the low finite strain achieved in the experiments which leads to weak wadsleyite cpo and to the diluting effect of added majorite the present experiments emphasize the importance of stress grain size evolution and water content in the forsterite to wadsleyite phase transformation and subsequent deformation in the transition zone

chalk porosity and sonic velocity versus burial depth influence of fluid pressure hydrocarbons and mineralogy seventy chalk samples from four formations in the overpressured danish central north sea have been analyzed to investigate how correlations of porosity and sonic velocity with burial depth are affected by varying mineralogy fluid pressure and early introduction of petroleum the results show that porosity and sonic velocity follow the most consistent depth trends when fluid pressure and pore volume compressibility are considered quartz content up to 10 has no marked effect but more than 5 clay causes lower porosity and velocity the mineralogical effect differs between p wave and shear velocity so that smectite bearing chalk has a high poisson s ratio in the water saturated case but a low value in the dry case oil bearing chalk has up to 25 units higher porosity than water saturated chalk at similar depth but similar velocity probably because hydrocarbons prevent pore filling cementation but not pore structure stiffening cementation in this presumably water wet chalk these results should improve the modeling of chalk background velocity for seismic inversion analysis when describing the porosity reducing process pore volume compressibility should probably be disregarded when correcting for fluid pressure because the cementing ions originate from stylolites which are mechanically similar to fractures we find that cementation occurs over a relatively short depth interval

reply to comment by a tommasi and d mainprice on visser et al 2008 probability of radial anisotropy in the deep mantle earth planet sci lett 270 2008 241 250

petrophysical properties of bioclastic platform carbonates implications for porosity controls during burial abstract this study is based on rock mechanical tests of samples from platform carbonate strata to document their petrophysical properties and determine their potential for porosity loss by mechanical compaction sixteen core plug samples including eleven limestones and five dolostones from miocene carbonate platforms on the marion plateau offshore northeast australia were tested at vertical effective stress 1 of 0 70 mpa as lateral strain was kept equal to zero the samples were deposited as bioclastic facies in platform top settings having paleo water depths of 1 50 mpa whereas six samples tested saturated with brine under drained conditions had up to 0 33 strain the yield strength was reached in five of the plugs the measured strains show an overall positive correlation with porosity vp ranges from 3640 to 5660 m s and vs from 1840 to 3530 m s poisson coefficient is 0 20 0 33 and young s modulus at 30 mpa ranged between 5 and 40 gpa water saturated samples had lower shear moduli and slightly higher p to s wave velocity ratios creep at constant stress was observed only in samples affected by pore collapse indicating propagation of microcracks although deposited as loose carbonate sand and mud the studied carbonates acquired reef like petrophysical properties by early calcite and dolomite cementation the small strains observed experimentally at 50 mpa indicate that little mechanical compaction would occur at deeper burial however as these rocks are unlikely to preserve their present high porosities to 4 5 km depth further porosity loss would proceed mainly by chemical compaction and cementation

support for the lunar cataclysm hypothesis from lunar meteorite impact melt ages lunar meteorites represent a more random sampling of lunar material than the apollo or luna collections and as such lunar meteorite impact melt ages are the most important data in nearly 30 years with which to reexamine the lunar cataclysm hypothesis within the lunar meteorite breccias mac 88105 que 93069 dag 262 and dag 400 seven to nine different impact events are represented with 40ar 39ar ages between 2 76 and 3 92 billion years ago ga the lack of impact melt older than 3 92 ga supports the concept of a short intense period of bombardment in the earth moon system at approximately 3 9 ga this was an anomalous spike of impact activity on the otherwise declining impact frequency curve

global azimuthal anisotropy in the transition zone surface wave dispersion measurements for love wave overtones carry evidence of azimuthal anisotropy in the transition zone of earth s mantle 400 to 660 kilometers deep a backus gilbert inversion of anisotropic phase velocity maps with resolution kernels mainly sensitive to the transition zone shows a robust long wavelength azimuthally anisotropic velocity structure this observation puts new constraints on the mineralogy and dynamics of the transition zone because this anisotropy may result from aligned minerals tilted laminated structures or even organized pockets of fluid inclusions

a three dimensional radially anisotropic model of shear velocity in the whole mantle summary we present a 3 d radially anisotropic s velocity model of the whole mantle saw642an obtained using a large three component surface and body waveform data set and an iterative inversion for structure and source parameters based on non linear asymptotic coupling theory nact the model is parametrized in level 4 spherical splines which have a spacing of 8 the model shows a link between mantle flow and anisotropy in a variety of depth ranges in the uppermost mantle we confirm observations of regions with vsh vsv starting at 80 km under oceanic regions and 200 km under stable continental lithosphere suggesting horizontal flow beneath the lithosphere we also observe a vsv vsh signature at 150 300 km depth beneath major ridge systems with amplitude correlated with spreading rate for fast spreading segments in the transition zone 400 700 km depth regions of subducted slab material are associated with vsv vsh while the ridge signal decreases whilethemid mantlehasloweramplitudeanisotropy vsv in the lowermost 300 km which appears to be a robust conclusion despite an error in our previous paper which has been corrected here the 3 d deviations from this signature are associated with the large scale low velocity superplumes underthecentralpacificandafrica suggestingthatvsh vsv isgeneratedinthepredominant horizontal flow of a mechanical boundary layer with a change in signature related to transition to upwelling at the superplumes

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

a two dimensional regional basin model of williston basin hydrocarbon systems institut francais du petrole s two dimensional model temispack is used to discuss the functioning of petroleum systems in the williston basin along a 330 km long section focusing on four regional source intervals ordovician yeoman formation lower devonian winnipegosis formation upper devonianulower mississippian bakken formation and mississippian lodgepole formation thermal history calibration against present temperature and source rock maturity profiles suggests that the williston basin can be divided into a region of constant heat flow of about 55 mw m2 away from the nesson anticline and a region of higher heat flow and enhanced thermal maturity in the vicinity of the nesson anticline original kinetic parameters used in the calibration were derived or each of the four source rocks from rock eval yield curves bakken overpressures are entirely due to oil generation not compaction disequilibrium very low bakken vertical permeabilities range from 0 01 to 0 001 nd are matched against observed overpressures whereas bakken porosities based on the model and confirmed by measurements are inferred to be also unusually low around 3 mature bakken shales do not seem to have reached hydraulic fractionation thresholds except perhaps locally in regions of extensional tectonic stress hydraulic fracturing cannot be viewed as a pervasive mechanism driving bakken oil expulsion our expulsion model confirms the high residual bakken oil saturations and explains the low residual s1 toc by the low bakken shale porosities approximately 85 of the oil generated in the bakken shales is predicted to have been expelled out of bakken strata which agrees with observed s1 toc trends madison group accumulations at the subcrop edge are found to be fed by lodgepole sourced oil only in particular by the rich middle lodgepole interval these accumulations probably result from a three dimensional migration pattern madison accumulations in the nesson anticline are found to be fed mostly by lodgepole sourced oil mixed with minor amounts of bakken sourced oil the vast majority of the expelled bakken oils are lost in the madison group at very low saturations this explains the low conventional oil resource associated with bakken sources by recent geochemical studies expulsion and migration occurred no earlier than the atest cretaceous paleocene in the yeoman and no earlier than the eocene in other source rocks consistent with temporal controls on oil migration flow models show no restriction to expulsion and migration of yeoman oil this suggests a potential undiscovered oil resource in ordovician and silurian strata of williston basin northeast of the nesson anticline

exposure history and terrestrial ages of ordinary chondrites from the dar al gani region libya we measured the concentrations of noble gases in 32 ordinary chondrites from the dar al gani dag region libya as well as concentrations of the cosmogenic radionuclides 14c 10be 26al 36cl and 41ca in 18 of these samples although the trapped noble gases in five dag samples show ratios typical of solar or planetary gases in all other dag samples they are dominated by atmospheric contamination which increases with the degree of weathering cosmic ray exposure cre ages of dag chondrites range from 1 myr to 53 myr the cre age distribution of 10 dag l chondrites shows a cluster around 40 myr due to four members of a large l6 chondrite shower the cre age distribution of 19 dag h chondrites shows only three ages coinciding with the main h chondrite peak at 7 myr while seven ages are 5 myr two of these h chondrites with short cre ages dag 904 and 908 show evidence of a complex exposure history five of the h chondrites show evidence of high shielding conditions including low 22ne 21ne ratios and large contributions of neutron capture 36cl and 41ca these samples represent fragments of two or more large pre atmospheric objects which supports the hypothesis that the high h l chondrite ratio at dag is due to one or more large unrecognized showers the 14c concentrations correspond to terrestrial ages 35 kyr similar to terrestrial ages of chondrites from other regions in the sahara but younger than two dag achondrites despite the loss of cosmogenic 36cl and 41ca during oxidation of metal and troilite concentrations of 36cl and 41ca in the silicates are also consistent with 14c ages 35 kyr the only exception is dag 343 h4 which has a 41ca terrestrial age of 150 40 kyr this old age shows that not only iron meteorites and achondrites but also chondrites can survive the hot desert environment for more than 50 kyr a possible explanation is that older meteorites were covered by soils during wetter periods and were recently exhumed by removal of these soils due to deflation during more arid periods such as the current one which started 3000 years ago finally based on the 26al 21ne and 10be 21ne systematics in 16 dag meteorites we derived more reliable estimates of the 10be 21ne production rate ratio which seems more sensitive to shielding than was predicted by the semi empirical model of graf et al 1990 but less sensitive than was predicted by the purely physical model of leya et al 2000

the record of cosmogenic radiogenic fissiogenic and trapped noble gases in recently recovered chinese and other chondrites abstract we performed a comprehensive study of the noble gas isotopic abundances in thirty six chondrites including twenty seven chondrites recovered in china the large data base allows us to recognize some new characteristics of the nuclear record in chondritic matter the comparison of the trapped noble gas release pattern for ordinary and carbonaceous chondrites shows that the planetary trapped noble gases in ordinary chondrites are released mainly above 1200 c whereas 85 of these gases in carbonaceous chondrites are degassed at 200 c there exists a clear correlation of the fraction of trapped xe released at 1200 c and petrologic type of chondrites it thus appears that the carrier phases of the trapped noble gases in ordinary and in carbonaceous chondrites may not be the same the ngawi ll3 chondrite is solar gas rich the solar gases in meteorites and lunar surface material are mixtures of solar wind sw and solar energetic particles sep we show that the variations of the 3 he 4 he and 20 ne 22 ne ratios for solar gas rich meteorites and lunar surface material could be either due to preferential diffusive losses of the lighter isotopes of he and ne or due to a change of the sw sep flux ratio with time furthermore we demonstrate that the 81kr concentration is a function of the shielding depth of a sample within the meteoroid deviations from this depth dependency curve are observed for jilin h5 lishui l5 suizhou l6 and dongtai ll6 a complex exposure history for jilin is thus confirmed and is possible for the other three chondrites cosmic ray exposure ages are calculated based on six different nuclides 3he 21ne 38ar 83kr 126xe and 81kr kr in most cases good agreement is observed for the ages derived from the different methods quality classes are assigned to the exposure ages and the age distributions are discussed in some meteorites we observe effects induced by secondary cosmicray produced neutrons epithermal neutron fluxes jn 30 300 ev and fast neutron fluxes jn 5 mev are derived based on the reactions 79br n 80kr and 24mg n 21ne respectively and preatmospheric masses of the meteoroids are estimated we show that the ratio j n 30 300 ev j n 5 mev increases with increasing preatmospheric mass we introduce a 3he exposure age 21ne exposure age vs 4he gas retention age 40ar gas retention age diagram that is a powerful tool for distinguishing different thermal histories of meteoroids finally in some chondrites we observe xe produced by 244pu fission and calculate the time span between fission xe retention in these chondrites and that of the angra dos reis achondrite we find that the ordinary chondrites started to retain fission xe 48 30 ma earlier than angra dos reis we do not observe systematic differences between h l and ll or type 5 and 6 chondrites with respect to the time of fission xe retention

isotope wallrock alteration associated with hypogene karst of the crimean piedmont ukraine although it is commonly perceived that isotopic alteration of carbonate rock is suppressed at low temperatures below ca 80 100 c this study demonstrates that alteration halos do develop in permeable limestones of relatively low textural maturity the study of paleogene carbonate bedrock constituting the walls of hypogene karst conduits of the crimean piedmont ukraine revealed several events of water rock interaction each resulting in isotopic alteration of the bedrock early development of hypogene karst conduits shifted 18o and 13c toward lower values by 1 2 and 1 3 respectively the width of the alteration zone locally exceeds several meters the case hardening associated with cavernous weathering shifted 18o and 13c of the bedrock toward slightly more positive values by up to 3 and 1 respectively the thickness of isotopic halos ranges from a few centimeters to tens of centimeters during late stage hypogene karstification the 18o values of the bedrock was shifted toward lower values by 5 6 forming a thin 5 15 mm alteration halo in most cases 13c was also shifted toward lower values by 6 9 but in one case a shift toward higher values by ca 2 was observed water involved in early hypogene karst and in the origin of cavernous weathering structures was enriched in 18 such waters are known in crimea in association with mud volcanoes on the kerch peninsula we suggest that similar deep seated water affected the crimean piedmont during the middle miocene water involved in late hypogene karstification had d values of 75 to 68 and 18o values of 10 to 9 fluid inclusion data similar to present day spring and well water in crimea isotopic calculations and fluid inclusion data indicate that the late hypogene karst processes occurred at low temperatures ca 50 c these processes ceased before 130 ka when the crimean piedmont was uplifted dissected by erosion and acquired its modern morphology

mechanical and chemical compaction model for sedimentary basin simulators abstract this article presents a sediment compaction model for sedimentary basin simulators the concepts previously used in sedimentary basin models are generalized and described in our model based on the formalism specific to rock and soil mechanics sediment compaction is described on a geological time scale by an elastoplastic model in which the elastic modulus and the strain hardening modulus increase when deformation increases the plastic limit is the maximum vertical effective stress reached by the sediment the rheology of the sediment is defined by a relationship that couples the porosity or volume of the sediment with the vertical effective stress assuming uniaxial deformation the model also incorporates a viscoplastic term in the compaction equation this component macroscopically considers viscous compaction phenomena such as pressure solution the viscosity coefficient is considered to be a function of the temperature some theoretical considerations allow us to conclude that the thermal dependency of the viscosity is given with an arrhenius law in which the activation energy ranges from 20 kj mole to 50 kj mole using viscosity coefficients extrapolated from previous laboratory experiments a sensitivity study shows significant effects of viscous deformation on the compaction of basins older than 1 ma in another study the viscosity coefficient is determined by matching the results of numerical simulations with laboratory and borehole data obtained from literature for chalk a constant viscosity coefficient of 2 5 gpa ma 8 1022 pa s has been determined assuming viscosity as a function of temperature with an activation energy of 40 kj mole chalk viscosity at 15 c is calibrated around 25 gpa ma simulations with different thermal gradients show that porosity is a function of the temperature furthermore simulations covering different lengths of time show that porosity is also a function of time

empirical relation between carbonate porosity and thermal maturity an approach to regional porosity prediction reply to brown discussion i thank ray 1985 for the interest shown in my paper schmoker 1984 his analysis illustrated mathematical relations not specifically addressed in my manuscript 1 do not believe however that these results are significant or that they weaken my arguments he demonstrated only the obvious point that if two variables correlate with a third variable they will correlate with each other further more his analysis and conclusions are based on the assumption of an exponential porosity depth relation i would argue that such a relation is an effect of subsurface diagenesis that does not explain the cause and that ray has approached the problem backward the proper con clusion would be that for certain simple basins an expo nential porosity depth relation follows logically from the idea that porosity decreases in the subsurface as a function of thermal maturation perhaps the point that should be emphasized here is that depth z in and of itself does not affect or control geologic

noble gases in 21 saharan ll chondrites exposure ages and possible pairings nineteen ll chondrites and two l ll chondrites adrar 003 and tanezrouft 010 from the saharan desert of algeria and libya have been analysed for their he ne and ar composition as well as for their abundance of 84kr and 132xe calculated 21ne cosmic ray exposure ages vary between 2 and 35 ma the age distribution is consistent with that of modern ll chondrite falls except that no dominant peaks can be observed especially not the one related to a 15 ma collisional event however the lack of young exposure ages of 8 ma is obvious this is a characteristic feature of ll chondrites only one of the 21 ll chondrites namely acfer 066 contains solar gases and is thus considered a regolith breccia three specimens reveal considerable loss of 3he probably due to periods of elevated temperatures in orbits with small perihelion distances furthermore severe loss of 4he and 40ar is found in two samples considering possible pairings we suggest 14 individual falls basically on the basis of the noble gas data the petrographic sub classification and by taking the find location into consideration however there are constraints on confirming pairings solely on the basis of our studies thus we can only exclude individual samples with a unique noble gas fingerprint from paired specimens

probability of radial anisotropy in the deep mantle article i nfo it is well established that the earth s uppermost mantle is anisotropic but observations of anisotropy in the deeper mantle have been more ambiguous radial anisotropy the discrepancy between love and rayleigh waves was included in the top 220 km of prem but there is no consensus whether anisotropy is present below that depth fundamental mode surface waves for commonly used periods up to 200 s are sensitive to structure in the first few hundred kilometers and therefore do not provide information on anisotropy below higher mode surface waves however have sensitivities that extend to and below the transition zone and should thus give insight about anisotropy at greater depths but they are very difficult to measure we previously developed a new technique to measure higher mode surface wave phase velocities with consistent uncertainties these data are used here to construct probability density functions of a radially anisotropic earth model down to approximately 1500 km in the uppermost mantle we obtain a high probability of faster horizontally polarized shear wave speed likely to be related to plate motion in the asthenosphere and transition zone however we find a high probability of faster vertically polarized shear wave speed to a depth of 1500 km in the lower mantle we see no significant shear wave anisotropy this is consistent with results from laboratory measurements which show that lower mantle minerals are anisotropic but lpo is unlikely to develop in the pressure temperature conditions present in the mid mantle 2008 elsevier b v all rights reserved

an interdisciplinary study of weathering effects in ordinary chondrites from the acfer region algeria weathering effects on meteorite finds from the acfer region were studied by various analytical techniques and in dependence on the depth of sampling in thin sections of weathered meteorites weathering effects usually decrease from the outside to the interior of the meteorite the results of evolved gas analysis indicate that variation in weathering between surface and core is not significant in respect to the formation of fe oxyhydroxides the secondary alteration effects in the noble gases are distributed unevenly throughout the specimens as seen in the nonsystematic differences observed for the heavy noble gases chemical analyses show significant enrichment of ba and sr in the outer parts of the weathered samples due to element contamination through aqueous solution iron ni and co are partly flushed from the system as the metal oxidation proceeds oxygen isotopes show increases in d180 and d17o with increasing terrestrial age for a set of h3 chondrites the degree of weathering determined from the water content was correlated with terrestrial ages and is discussed with respect to possible weathering mechanisms

new noble gas data of primitive and differentiated achondrites including northwest africa 011 and tafassasset this work reports on the noble gas inventory of 3 new acapulcoites 3 brachinites 2 new eucrites from the dar al gani region in libya the unique achondrite dar al gani dag 896 from the same locality the new eucrite like achondrite northwest africa nwa 011 and the controversial sample tafassasset we determined cosmic ray exposure and gas retention ages evaluated shielding conditions and discuss the trapped noble gas component of the specimens all exposure ages are within the known range of stony meteorites and partly confirm previously established age clusters shielding conditions vary suggesting substantial shielding for all 3 brachinites and tafassasset we cannot exclude however that the mg rich composition of brachinites simply simulates heavy shielding regarding the trapped component we found q like compositions only for the acapulcoite thiel mountains til 99002 the brachinite elephant moraine eet 99402 yields a high subsolar 36ar 132xe ratio of 400 along with a slightly elevated 84kr 132xe ratio indicating minor atmospheric contamination all the other samples particularly the eucrite dag 983 are characterized by clearly elevated ar kr xe ratios due to significant terrestrial alteration tafassasset exhibits noble gas parameters that are different from those of cr chondrites including a relatively high cosmic ray exposure age the absence of a solar component low 132xe concentrations a low trapped 36ar 132xe ratio of 30 and a noticeable amount of radiogenic 129xe similar attributes have been observed for some primitive achondrites these attributes are also consistent with the metamorphic character of the sample we therefore consider tafassassets noble gas record to be inconclusive as to its classification primitive achondrite versus metamorphosed cr chondrite

the kumtag 016 l5 strewn field xinjiang province china the kumtag 016 strewn eld was found in the eastern part of the kumtag desert xinjiang province china in this study 24 recovered meteorites have been ch aracterized by a suite of different analytical techniques to investigate their petrography mineralogy bulk trace elements noble gas isotopic composition density and porosity we attribute to the strewn eld 22 l5 chondrites with shock stage s4 and weathering grade w2 w3 two differen t meteorites kumtag 021 an l4 chondrite and kumt ag 032 an l6 chondrite were recognized within the strewn eld area moreover kumt ag 003 an h5 chondrite was previously found in the same area we infer that the kumtag 016 strewn eld most likely consists of at least four distinct meteorite falls the effects of terrestrial weathering on the studied mete orites involve sul de metal alteration chemical changes sr ba pb and u enrichments and depletion in cr co ni and cs abun dances and physical modi cations decrease of grain density and porosity measurements of the light noble gases indicate that the analyzed kumtag l5 samples contain solar wind implanted noble gases with a ne ne ratio of 12 345 the cosmic ray exposure cre ages of the l5 ch ondrites are in a narrow range 3 6 1 4 ma to 5 2 0 4 ma for l4 cho ndrite kumtag 021 and l6 chondrite kumtag 032 the cre ages are 5 9 0 4 ma and 4 7 0 8 ma respectively

experimental simulation of chemomechanical processes during deep burial diagenesis of carbonate rocks chemomechanical processes involved in the deep burial diagenesis of carbonate petroleum reservoirs are still poorly understood to better understand these processes and explain how porosity and permeability can be preserved at the great depth of dbrs deeply buried reservoirs we developed an experimental device allowing both the simulation of high pressure stresses temperature conditions 80 c 60 mpa of confining pressure and differential stress up to 40 mpa of dbr and the circulation of different fluids in rock samples we tested triaxial multistep creep tests four core samples of a cemented limestone and analyzed creep deformations fluids chemistry and petrographical and petrophysical properties of samples different flow conditions no flow and flow through and chemical compositions natural meteoric water with and without phosphate ions were considered our study showed that the precipitation of calcite on free pore walls of micrites blocks the microporosity between micrite crystals thus rendering the microporosity inaccessible to fluids hence the connected porosity decreased strongly after experimentation this is due to the psc pressure solution creep which is the main process implied in the porosity reduction of a carbonate rock during deep burial the preservation of macropores during psc allows the preservation of permeability in addition calcite solubility is positively dependent on mechanical parameters axial compaction and axial stress thus suggesting that calcite can precipitate during decompression of deep basinal fluids resulting in changes in porosity a comparison of experimental results with theoretical calculations showed that the integration of the psc process into calculation databases would greatly improve the modeling of dbr

viscoplastic self consistent and equilibrium based modeling of olivine lattice preferred orientations implications for the upper mantle seismic anisotropy anisotropy of upper mantle physical properties results from lattice preferred orientation lpo of upper mantle minerals in particular olivine we use an anisotropic viscoplastic self consistent vpsc and an equilibrium based model to simulate the development of olivine lpo and hence of seismic anisotropy during deformation comparison of model predictions with olivine lpo of naturally and experimentally deformed peridotites shows that the best fit is obtained for vpsc models with relaxed strain compatibility slight differences between modeled and measured lpo may be ascribed to activation of dynamic recrystallization during experimental and natural deformation in simple shear for instance experimental results suggest that dynamic re crystallization results in further reorientation of the lpo leading to parallelism between the main 010 100 slip system and the macroscopic shear thus modeled simple shear lpos are slightly misoriented relative to lpos measured in natural and experimentally sheared peridotites this misorientation is higher for equilibrium based models yet seismic properties calculated using lpo simulated using either anisotropic vpsc or equilibrium based models are similar to those of naturally deformed peridotites errors in the prediction of the polarization direction of the fast s wave and of the fast propagation direction for p waves are usually 15 moreover overestimation of lpo intensities in equilibrium based and vpsc simulations at high strains does not affect seismic anisotropy estimates because these latter are weakly dependent on the lpo intensity once a distinct lpo pattern has been developed thus both methods yield good predictions of development of upper mantle seismic anisotropy in response to plastic flow two notes of caution have nevertheless to be observed in using these results 1 the dilution effect of other upper mantle mineral phases in particular enstatite has to be taken into account in quantitative predictions of upper mantle seismic anisotropy and 2 lpo patterns from a few naturally deformed peridotites cannot be reproduced in simulations these abnormal lpos represent a small percent of the measured natural lpos but the present sampling may not be representative of their abundance in the earth s upper mantle

pressure sensitivity of olivine slip systems and seismic anisotropy of earth s upper mantle the mineral olivine dominates the composition of the earth s upper mantle and hence controls its mechanical behaviour and seismic anisotropy experiments at high temperature and moderate pressure and extensive data on naturally deformed mantle rocks have led to the conclusion that olivine at upper mantle conditions deforms essentially by dislocation creep with dominant 100 slip the resulting crystal preferred orientation has been used extensively to explain the strong seismic anisotropy observed down to 250 km depth the rapid decrease of anisotropy below this depth has been interpreted as marking the transition from dislocation to diffusion creep in the upper mantle but new high pressure experiments suggest that dislocation creep also dominates in the lower part of the upper mantle but with a different slip direction here we show that this high pressure dislocation creep produces crystal preferred orientations resulting in extremely low seismic anisotropy consistent with seismological observations below 250 km depth these results raise new questions about the mechanical state of the lower part of the upper mantle and its coupling with layers both above and below

plastic flow of pyrope at mantle pressure and temperature despite the abundance of garnet in deforming regions of the earth such as subduction zones its rheological properties are not well defined by laboratory measurements here we report measurements of steady state plastic properties of pyrope in its stability field temperature up to 1573 k pressure up to 6 8 gpa strain rate approx 10 5 s 1 using a deformation dia apparatus d dia coupled with synchrotron radiation synthetic pyrope py100 and natural pyrope py70alm16gr14 are both studied in a dry environment transmission electron microscopy tem investigation of the run products indicates that dislocation glide assisted by climb within grains and dynamic recrystallization for grain boundary strain accommodation is the dominant deformation process in pyrope both synthetic and natural pyropes stress and strain rate data as measured in situ by x ray diffraction and imaging are best fitted with the single flow law

comment on the article probability of radial anisotropy in the deep mantle by visser et al 2008 epsl 270 241 250 0012 821x see front matter 2008 elsevier b v al doi 10 1016 j epsl 2008 07 061 based on the inversion of a large surface waves dataset including both fundamental and higher modes visser et al 2008 constructed new maps of the probability of surface wave polarization or radial anisotropy these maps bring new constraints on the variation of radial anisotropy with depth as a function of the geodynamic environment however the interpretation of the seismic anisotropy distribution in terms of mantle deformation is oversimplified since it is essentially based on data of the evolution of olivine crystal preferred orientations and seismic anisotropy at high temperature but low pressure conditions neglecting recent findings on the deformation of mantle minerals under high pressure in situ mantle conditions three points in particular deserve a throughout discussion since they highlight the limitations of using basic concepts that have been established from the analysis of shallow mantle rocks and low pressure deformation experiments as for instance i lack of anisotropy implies deformation by diffusion creep or ii fast polarization or propagation for p or sv waves directions mark systematically the flow direction to interpret seismic anisotropy data below depths of 200 250 km in the mantle

predicted glide systems and crystal preferred orientations of polycrystalline silicate mg perovskite at high pressure implications for the seismic anisotropy in the lower mantle abstract we use first first principle methods and the peierls nabarro model to evaluate the resistance to glide characterized by the peierls stress of glide systems for end member mgsio 3 perovskite at mantle pressures 010 100 is the easiest glide system in mg perovskite at all pressures peierls stresses increase systematically with pressure for all systems except 001 010 indicating the importance of lattice friction at lower mantle pressures the ratio of the maximum peierls stress for each system relative to the 010 100 value defines their critical resolved shear stress crss these crss are used in a visco plastic self consistent homogenization model to predict the evolution of crystal preferred orientations cpo during deformation of polycrystalline mg perovskite in axial compression 100 tends to align with the compression direction in agreement with in situ observations in axial compression experiments in simple shear 010 concentrates near the shear direction and 100 although more dispersed tends to align near the shear plane consistent with the dominant activity of the easier 010 100 system the calculated seismic anisotropy for a 100 mg perovskite aggregate using the cpo in simple shear and the elastic constants of mgsio 3 perovskite at lower mantle pressures and temperatures is weak 3 for p waves with and 2 for s waves and decreases with increasing temperature and pressure p waves show the fastest propagation parallel to the lineation and s waves fast polarization is in the foliation at 38 gpa and normal to the lineation at 88 gpa this weak anisotropy is consistent with global seismological observations of a nearly isotropic lower mantle there are however two regions where strain induced mg perovskite cpo could contribute to anisotropy a low temperature regions in the uppermost lower mantle where the predicted s wave polarization anisotropy may attain 1 6 with a fast polarization parallel to the foliation b in high high temperature domains in the d layer where mg perovskite may be the major stable phase leading to polarization of fast s waves normal to the lineation for propagation directions at high angle to the lineation and an apparent isotropy for all other propagation directions

empirical relation between carbonate porosity and thermal maturity an approach to regional porosity prediction data indicate that porosity loss in subsurface carbonate rocks can be empirically represented by the power function thgr a tti b where thgr is regional porosity tti is lopatin s time temperature index of thermal maturity the exponent b equals approximately 0 372 and the multiplier a is constant for a given data population but varies by an order of magnitude overall implications include the following 1 the decrease of carbonate porosity by burial diagenesis is a maturation process depending exponentially on temperature and linearly on time 2 the exponent b is essentially independent of the rock matrix and may reflect rate limiting processes of diffusive transport 3 the multiplying coefficient a incorporates the net effect on porosity of all depositional and diagenetic parameters within constraints carbonate porosity prediction appears possible on a regional measurement scale as a function of thermal maturity estimation of carbonate porosity at the time of hydrocarbon generation migration or trapping also appears possible

strain induced seismic anisotropy of wadsleyite polycrystals and flow patterns in the mantle transition zone 1 we use forward models based on recent high pressure experimental data on mantle minerals to predict the seismic anisotropy produced by plastic strain of orthorhombic wadsleyite the dominant mineral in the upper transition zone these models predict a weak seismic anisotropy for a polycrystal of pyrolitic composition 60 wadsleyite 40 garnet at transition zone conditions 2 for p and 1 for s waves for a shear strain of 1 both p and s wave anisotropy patterns show an orthorhombic symmetry p waves propagate faster at low angle to the shear direction and slower at high angle to the shear plane s wave anisotropy is characterized by faster propagation of waves polarized at low angle to the shear direction horizontal shearing results therefore in higher velocities for horizontally propagating p waves ph and horizontally polarized s waves sh as well as in weak azimuthal variation of sv and sh velocities on the other hand vertical flow leads to higher velocities for vertically propagating p waves pv and vertically polarized s waves sv and to a weak azimuthal variation of sv velocity but to a roughly constant sh velocity analysis of global observations of seismic anisotropy in the transition zone in the light of these models supports dominant horizontal flow in the uppermost transition zone in agreement with predictions of geodynamical models that explicitly introduce phase transitions

predicted elastic properties of the hydrous d phase at mantle pressures implications for the anisotropy of subducted slabs near 670 km discontinuity and in the lower mantle the dense hydrous magnesium silicate called the d phase is the most likely candidate to recycle hydrogen into the lower mantle in subduction zones as seismology represents the preferred method to detect this mineral in subduction zones the single crystal elastic tensor has been calculated using first principle methods a triple cell p3 m1 was used to account for an ordered ideal composition of the d phase to lower mantle pressures the elastic tensor of the mineral at ambient conditions is predicted to be c11 387 7 c33 287 7 c44 100 4 c12 108 0 c13 51 1 c14 14 6 in gpa with bulk modulus at zero pressure ko 163 gpa and a statistical error of about 4 0 gpa for all constants the pressure derivatives of the elastic constants have been determined to pressure of 80 gpa our tensor correctly predicts the published experimental measurements of linear compressibility along the a and c axes the logarithmic pressure derivative of the c a axial ratio and bulk modulus at zero pressure it contradicts the experimentally measured elastic tensor reported by liu l g okamoto k yang y j chen c c lin c c 2004 elasticity of single crystal phase d a dense hydrous magnesium silicate by brillouin spectroscopy solid state commun 132 517 520 which fails to reproduce the experimental compressibility data using the elastic constants and density predicted to 85 gpa the seismic anisotropy of p and s waves has been calculated as a function of pressure the single crystal has high p wave velocities and shear wave splitting in the basal plane below 20 gpa at high pressures the maximum p wave velocities have threefold symmetry normal to a axes in the basal plane whereas the maximum shear wave splitting is parallel to a axes with twofold symmetry the d phase has high vp and vs anisotropy at ambient pressure 17 6 for vp and 19 9 for vs the vp anisotropy decreases with increasing pressure to about 30 gpa while it remains constant at 8 from 30 to 85 gpa the vs anisotropy decreases to 17 at 20 gpa and then increases to 22 at 85 gpa the isotropic velocity ratios of s to p rs p bulk sound to s r s and density to s r s are calculated as a function of pressure the rs p shows very little variation with pressure with low value of 0 6 whereas both r s and r s increase with pressure to peak values of 2 8 and 2 0 respectively at about 60 gpa the presence of the d phase in subducted horizontal stagnant plates in the circum pacific could contribute to a number of seismic observations such as the observed velocity heterogeneity at depths between 500 and 1000 km and the fast s waves travelling horizontally with horizontal polarization in this depth range further the lower density of the d phase compared with

probability density functions for radial anisotropy implications for the upper 1200 km of the mantle the presence of radial anisotropy in the upper mantle transition zone and top of the lower mantle is investigated by applying a model space search technique to rayleigh and love wave phase velocity models probability density functions are obtained independently for s wave anisotropy p wave anisotropy intermediate parameter r vp vs and density anomalies the likelihoods for p wave and s wave anisotropy beneath continents cannot be explained by a dry olivine rich upper mantle at depths larger than 220 km indeed while shear wave anisotropy tends to disappear below 220 km depth in continental areas p wave anisotropy is still present but its sign changes compared to the uppermost mantle this could be due to an increase with depth of the amount of pyroxene relative to olivine in these regions although the presence of water partial melt or a change in the deformation mechanism cannot be ruled out as yet a similar observation is made for old oceans but not for young ones where vsh s vsv appears likely down to 670 km depth and vph s vpv down to 400 km depth the change of sign in p wave anisotropy seems to be qualitatively correlated with the presence of the lehmann discontinuity generally observed beneath continents and some oceans but not beneath ridges parameter r shows a similar age related depth pattern as shear wave anisotropy in the uppermost mantle and it undergoes the same change of sign as p wave anisotropy at 220 km depth the ratio between dlnvs and dlnvp suggests that a chemical component is needed to explain the anomalies in most places at depths greater than 220 km more tests are needed to infer the robustness of the results for density but they do not affect the results for anisotropy

deformation and mantle flow beneath the sangihe subduction zone from seismic anisotropy abstract subduction of oceanic lithosphere is the most direct feedback between the earth s surface and deep interior however the detail of its interaction with the broader convecting mantle is still unclear mantle flow around subduction zones can be constrained using seismic anisotropy but despite many such studies a simple global picture is lacking the sangihe subduction zone where the molucca sea microplate is subducting westward beneath the eurasian plate is part of the tectonically complex sulawesi philippine region and an ideal natural laboratory to study complex subduction processes we investigate the anisotropic structure of the sangihe subduction zone with shear wave splitting measurements of local s and sks phases at two stations mni in sulawesi dav in the philippines as well as downgoing s phases at five stations at teleseismic distances combining different phases allows a better vertical resolution of anisotropic fabrics than is possible with a single phase the broad depth distribution of local events 60 630 km allows us to observe a change in splitting behaviour at 380 km depth above fast directions are trench parallel and delay times t are 0 34 0 53 s with no increase with depth we suggest this anisotropy is caused by aligned cracks possibly melt filled beneath the volcanic arc and fossil anisotropy in the overriding plate below 380 km is predominantly trench normal and t are slightly higher 0 53 0 65 s as no correlation is observed with inferred distance travelled inside the slab we attribute this anisotropy to shear layers atop the slab which are coherent from 200 to 400 km depth and perhaps extend into the transition zone sks and source side measurements show larger t 1 53 and 1 33 s respectively and trench parallel since these phases predominantly sample sub slab mantle we consider along strike lateral flow associated with the double sided subduction of the molucca sea microplate to be the most likely explanation we thus infer three dominant regions of anisotropy at the sangihe subduction zone one within the overriding lithosphere one along the slab wedge interface and one below the subducting molucca sea slab the mantle wedge above 200 km depth and the slab itself do not seem to contribute notably to the measured anisotropy this study demonstrates the insight seismic anisotropy can provide into mantle dynamics even in tectonically complex subduction systems

pressure solution and hydrothermal recrystallization of carbonate sediments an experimental study reply abstract the extent of calcite recrystallization was determined in pressure solution and hydrothermal experiments which were conducted on deep sea carbonates of low mg calcite iceland spar and reagent grade calcite powder in the pressure solution experiments wet sediments were subjected to confining pressures of 500 1500 bars and pore pressures of 150 500 bars at temperatures between 22 and 180 c for 21 240 h the hydrothermal experiments were performed in sealed teflon coated bombs at 200 c zero effective stress in sulfate free sea water for two weeks the hydrothermal system was solution dominated the extent of calcite recrystallization was determined by measuring the oxygen isotopic compositions of the pore fluids and solids before and after each experiment scanning electron microscope observations porosity and specific surface area measurements were performed in fine grained carbonate samples subjected to high effective stresses the mechanism for recrystallization apparently involves both relief of strain energy at grain to grain contacts and decrease in surface free energy by decreasing the surface area while in coarse grained carbonates relief of strain energy appears to be the most important control of recrystallization in the hydrothermal experiments however decrease in surface free energy is the only driving force for recrystallization effective stress increased the rate of calcite recrystallization in both pressure solution and hydrothermal experiments clay minerals retarded the reaction the effects of diatomite and basaltic glass on the extent of calcite recrystallization was investigated only in the hydrothermal experiments both admixed non carbonate materials retarded the reaction diatomite being the most effective inhibitor surface chemical reactions seem to be responsible for the observed inhibitions of calcite recrystallization increases in the extent of calcite recrystallization with increasing ionic strength were observed in hydrothermal experiments in nacl solutions of five different ionic strengths

noble gases in enstatite chondrites ii the trapped component the trapped noble gas record of 57 enstatite chondrites e chondrites has been investigated basically two different gas patterns have been identified dependent on the petrologic type all e chondrites of type 4 to 6 show a mixture of trapped common chondritic rare gases q and a subsolar component range of elemental ratios for e4 6 chondrites 36ar 132xe 582 270 and 36ar 84kr 242 88 e3 chondrites usually contain q gases but also a composition with lower 36ar 132xe and 36ar 84kr ratios which we call sub q 36ar 132xe 37 0 18 0 and 36ar 84kr 41 7 18 1 the presence of either the subsolar or the sub q signature in particular petrologic types cannot be readily explained by parent body metamorphism as postulated for ordinary chondrites we therefore present a different model that can explain the bimodal distribution and composition of trapped heavy noble gases in e chondrites trapped solar noble gases have been observed only in some e3 chondrites about 30 of each group eh3 and el3 chondrites amounting to 9 of all analyzed e chondrites show the solar signature notably only one of those meteorites has been explicitly described as a regolith breccia

new findings for the equilibrated enstatite chondrite grein 002 we report new petrographic and chemical data for the equilibrated el chondrite grein 002 including the occurrence of osbornite metallic copper abundant taenite and abundant diopside as inferred from low si concentrations in kamacite the presence of ferroan alabandite textural deformation chemical equilibration of mafic silicates and a subsolar noble gas component we concur with grein 002s previous classification as an el4 5 chondrite furthermore the existence of pockets consisting of relatively coarse euhedral enstatite crystals protruding large patches of fe ni alloys suggests to us that this el4 5 chondrite has been locally melted we suspect impact induced shock to have triggered the formation of the melt pockets mineralogical evidence indicates that the localized melting of metal and adjacent enstatite must have happened relatively late in the meteorites history the deformation of chondrules equilibration of mafic silicates and generation of normal zoning in fe zn sulfides took place during thermal alteration before the melting event following parent body metamorphism daubreelite was exsolved from troilite in response to a period of slow cooling at subsolidus temperatures exsolution of schreibersite from the coarse metal patches probably occurred during a similar period of slow cooling subsequent to the event that induced the formation of the melt pockets overall shock features other than localized melting correspond to stage s2 and were likely established by the final impact that excavated the grein 002 meteoroid

noble gases in enstatite chondrites i exposure ages pairing and weathering effects cosmic ray exposure ages calculated from cosmogenic noble gas nuclides are reported for 57 enstatite e chondrites 43 of them were measured for the first time with a total of 62 individual e chondrites literature and this data corrected for pairing the observed spectrum of ages ranges between 0 07 and 66 ma three clusters seem to develop at about 3 5 8 and 25 ma respectively since the uncertainty of ages is estimated to be 20 in contrast to 10 to 15 for ordinary chondrites and the number of examined samples is still comparatively small these peaks have to be confirmed by more measurements regarding the two subgroups eh and el chondrites no systematic trend is apparent in the distribution of cosmic ray exposure ages several e chondrites yield significantly lower 38ar ages compared to those calculated from cosmogenic 3he and 21ne for these e chondrites we suggest a reduction of cosmogenic 38ar as a result of weathering in order to prove the possible influence of terrestrial alteration on the cosmogenic noble gas record of e chondritic material we simulated terrestrial weathering in an experiment of 12 weeks duration the treatment showed that a significant amount of cosmogenic 38ar is lost on earth by the influence of water

noble gas record and cosmic ray exposure history of the new co3 chondrite moss comparison with lance and other co chondrite falls abstract the moss meteorite is the first co chondrite fall after a time period of 70 yr and the least terrestrially contaminated member of its group its cosmic ray exposure cre age t3 13 5 ma t21 14 6 ma is distinct among co chondrites and within witnessed falls is the shortest after lance which we have reanalyzed gas retention ages are approximately 3 95 109 yr u th he and approximately 4 43 109 yr k ar respectively trapped ar kr and xe are present in moss in abundances typical for co chondrites with planetary elemental and isotopic compositions presence of hl xenon from presolar diamonds is observed in the stepwise release analysis of lance it may also be present in moss but it is difficult to ascertain in single step bulk analyses it follows from our new data combined with a survey of the literature that the abundance of trapped gases in co chondrites is not a good indicator of their petrological subtype

the non trivial problem of meteorite pairing pairing is the procedure of identifying fragments of a single meteorite fall that were separated during atmospheric passage or during terrestrial history by establishing the similarity of two or more meteorite fragments we argue that pairing is governed by two principles that only a single mismatch of properties is required to refute a proposed pairing and that virtually all pairings bear some degree of uncertainty using data distributions for modern falls we take a probability approach to estimate degrees of certainty associated with proposed pairings emphasizing the importance of unusual features for new pairing criteria or new analytical additions to old criteria the degree of variation within individual meteorites must be delineated and the degree of variation within meteorite classes must be quantified criteria for pairing can be divided into 1 parent body history indicators 2 meteoroid space history indicators and 3 terrestrial history indicators included in these categories are 11 specific criteria including petrographic textures mineralogy and mineral composition terrestrial age estimates cosmic ray exposure ages and natural thermoluminescence tl levels not all criteria are applicable to all meteorite types about 2275 pairings suggested in the literature have been subjected to this analysis many literature pairings especially those involving common meteorite types bear large uncertainties due to lack of data

crystal preferred orientations of garnet comparison between numerical simulations and electron back scattered diffraction ebsd measurements in naturally deformed eclogites observations of dislocations sub grains and elongated crystal shapes support plastic deformation of garnet in laboratory experiments and naturally deformed eclogites to evaluate the crystal preferred orientations cpo of garnet formed in axial shortening pure shear and simple shear we performed numerical simulations of cpo development during plastic flow using the visco plastic self consistent model as input for the models we use the slip systems determined by transmission electron microscopy using experimentally deformed specimens although in garnet 66 slip systems are available slip on the k111l 110 system provides over 86 of the total strain in the simulations characteristic cpo distributions are produced for the three deformation paths with the cpo being strongest for axial shortening and weakest for simple shear compared with low symmetry minerals the pole figure densities of garnet which has cubic symmetry are weak k100l axes tend to align with the shortening direction in all three deformation modes the simulations are compared with cpo of naturally deformed garnet from nine eclogite samples from the alps norway and mali which contain 20 40 garnet all samples show weak garnet cpo only two samples have a cpo pattern similar to the simulations for simple shear no samples are similar to simulations for axial strain or pure shear the presence of other weaker minerals such as omphacite and quartz with volume fractions higher than garnet probably prevented garnet from becoming highly strained and developing characteristic cpos in these eclogites higher volume fractions of garnet and higher temperature conditions may however allow the development of garnet cpo in the mantle transition zone particularly within subducted oceanic material morb q 2004 published by elsevier ltd

non nucleosynthetic heterogeneity in non radiogenic stable hf isotopes implications for early solar system chronology abstract nucleosynthetic heterogeneity and secondary neutron capture reactions may have important implications for 176 lu 176 hf chronology and modelling of early planetary evolution so far the relevance of these phenomena for the lu hf system has not been explored we therefore have analyzed the non radiogenic stable hf isotope composition 177 hf 178 hf 179 hf and 180 hf of meteorites meteorite components and terrestrial rock samples to identify nucleosynthetic or neutron capture induced variations all analyzed chondrites have uniform 178 hf 177 hf and 180 hf 177 hf values that cannot be resolved from the average terrestrial composition thus there is no evidence for nucleosynthetic heterogeneity in chondrites or earth and these data support the use of a chondritic reference value for the hf isotope composition of the bulk silicate earth this homogeneity contrasts with nucleosynthetic heterogeneities found in lighter elements and provides evidence for a separate synthesis of light and heavy r process nuclei various mesosiderite samples and one lunar meteorite display coupled 178 hf 177 hf and 180 hf 177 hf anomalies that are associated with neutron capture induced deviations in 149 sm 154 sm and 150 sm 154 sm however the analyzed chondrites and an aubrite show only sm isotope anomalies and these are the result of neutron capture the hf isotope anomalies require substantial capture of epithermal neutrons whereas sm anomalies result primarily from thermal neutron capture the non radiogenic stable isotope composition of hf is thus a suitable monitor for epithermal neutron capture reactions the data reveal distinct neutron energy spectra mesosiderites are characterized by high epithermal to thermal neutron fluence ratios whereas the remaining samples show low epithermal to thermal ratios secondary neutron capture may significantly increase the measured 176 hf 177 hf in whole rock meteorite samples without causing a resolvable shift in 176 lu 177 hf thus it could potentially induce scatter in lu hf whole rock isochrons and produce spurious initial 176 hf 177 hf values however the slopes of internal i e mineral isochrons cannot be increased significantly by secondary neutron capture this process therefore cannot account for the unrealistically old 176 lu 176 hf ages e g 4 75 ga of some meteorites

in situ observation of texture development in olivine ringwoodite magnesiowustite and silicate perovskite at high pressure magnesium silicates are the dominant minerals in the earth s mantle their preferred orientation is important for understanding the rheology and seismic anisotropy in the deep earth here we report results of radial synchrotron diffraction diamond anvil cell dac experiments on san carlos olivine axially compressed to 50 gpa experiments were performed at room temperature except for brief laser heating to induce phase transformations high stresses and development of preferred orientation were observed in diffraction images quantitative texture information was obtained by analyzing the images with the rietveld method with increasing pressure between 9 and 43 gpa olivine develops a texture with 001 axes perpendicular to the compression direction that is compatible with hk0 001 pencil glide ringwoodite between 20 and 50 gpa develops weak preferred orientation with 011 lattice planes perpendicular to the compression direction after the phase transformation perovskite and magnesiowqstite display transformation textures that are then modified by continuing deformation magnesiowqstite has a weak h111i maximum parallel to the compression direction that changes towards h001i with increasing deformation perovskite transforming from olivine has a pronounced 100 transformation texture and with increasing deformation a 012 maximum develops the transformation texture is probably produced by mechanical 110 twinning and nucleation in orientations that minimize elastic strain energy the deformation texture of perovskite is due to slip d 2004 elsevier b v all rights reserved

water partitioning between nominally anhydrous minerals in the mgo sio2 h2o system up to 24 gpa implications for the distribution of water in the earth s mantle multi anvil experiments have been conducted in the mgo sio2 h2o system at pressures of 15 24 gpa and temperatures of 1200 1600 c to investigate the partitioning of water between mantle phases the water contents were obtained from fourier transform infrared spectroscopy on doubly polished and clear crystals most of the mineral phases coexisted with a hydrous melt the results show that among all magnesium silicate phases 1 mgsio3 perovskite is the only phase which does not dissolve a detectable amount of water and 2 the high pressure polymorphs of mg2sio4 wadsleyite and ringwoodite dissolve about one order of magnitude more water than the polymorphs of mgsio3 clinoenstatite majorite and akimotoite the following partition coefficients of water were measured dwadsleyite clinoenstatite 3 8 at 15 gpa and 1300 c dringwoodite akimotoite 21 at 19 gpa and 1300 c dakimotoite perovskite 1 at 24 gpa and 1600 c and dpericlase perovskite 1 at 24 gpa and 1500 c these results suggest that most of the water in the earth s mantle is partitioned in the transition zone

the vicencia meteorite fall a new unshocked s1 weakly metamorphosed 3 2 ll chondrite the vicencia meteorite a stone of 1 547 kg fell on september 21 2013 at the village borracha near the city of vicencia pernambuco brazil it was recovered immediately after the fall and our consortium study showed it to be an unshocked s1 ll3 2 ordinary chondrite the ll group classification is based on the bulk density 3 13 g cm 3 the chondrule mean apparent diameter 0 9 mm the bulk oxygen isotopic composition delta 17 o 3 768 pm0 042 text o mkern 5mu mkern 3mu text oo delta 18 o 5 359 pm0 042 text o mkern 5mu mkern 3mu text oo delta 17 o 0 981 pm 0 020 text o mkern 5mu mkern 3mu text oo the content of metallic fe ni 1 8 vol the co content of kamacite 1 73 wt the bulk contents of the siderophile elements ir and co versus au and the ratios of metallic fe 0 total iron 0 105 versus total fe mg 1 164 and of ni mg 0 057 versus total fe mg the petrologic type 3 2 classification is indicated by the beautifully developed chondritic texture the standard deviation 0 09 versus mean cr 2 o 3 content 0 14 wt of ferroan olivine the tl sensitivity and the peak temperature and peak width at half maximum the cathodoluminescence properties of chondrules the content of trapped 132 xe tr 0 317 10 8 cm 3 stp g 1 and the raman spectra for organic material in the matrix the cosmic ray exposure age is 72 ma which is at the upper end of the age distribution of ll group chondrites the meteorite is unusual in that it contains relatively large up to nearly 100 m in size secondary fayalite grains defined as olivine with fa textgreater 75 large enough to allow in situ measurement of oxygen and mn cr isotope systematics with sims its oxygen isotopes plot along a mass dependent fractionation line with a slope of 0 5 and delta 17o of 4 0 pm 0 3 text o mkern 5mu mkern 3mu text oo and are similar to those of secondary fayalite and magnetite in the unequilibrated chondrites eet 90161 met 96503 and ngawi these data suggest that secondary fayalite in vicencia was in equilibrium with a fluid with a delta 17 o of 4 text o mkern 5mu mkern 3mu text oo consistent with the composition of the fluid in equilibrium with secondary magnetite and fayalite in other unequilibrated ordinary chondrites secondary fayalite and the chondrule olivine phenocrysts in vicencia are not in isotopic equilibrium consistent with low temperature formation of fayalite during aqueous alteration on the ll parent body that alteration as dated by the 53 mn 53 cr chronology age of secondary fayalite took place 4 0 1 4 1 1 ma after formation of cv cais when anchored to the quenched angrite d orbigny

pressure induced slip system transition in forsterite single crystal rheological properties at mantle pressure and temperature deformation experiments were carried out in a deformation dia high pressure apparatus d dia on oriented mg2sio4 olivine fo100 single crystals at pressure p ranging from 2 1 to 7 5 gpa in the temperature t range 1373 1677 k and in dry conditions these experiments were designed to investigate the effect of pressure on olivine dislocation slip system activities responsible for the lattice preferred orientations observed in the upper mantle two compression directions were tested promoting either 100 slip alone or 001 slip alone in 010 crystallographic plane constant applied stress sigma and specimen strain rates formula were monitored in situ using time resolved x ray synchrotron diffraction and radiography respectively transmission electron microscopy tem investigation of the run products reveals that dislocation creep assisted by dislocation climb and cross slip was responsible for sample deformation a slip transition with increasing pressure from a dominant 100 slip to a dominant 001 slip is documented extrapolation of the obtained rheological laws to upper mantle p t and sigma conditions suggests that 001 slip activity becomes comparable to 100 slip activity in the deep upper mantle while 001 slip is mostly dominant in subduction zones these results provide alternative explanations for the seismic anisotropy attenuation observed in the upper mantle and for the puzzling seismic anisotropy anomaliesmore commonly observed in subduction zones less