an automated time window selection algorithm for seismic tomography we present flexwin an open source algorithm for the automated selection of time windows on pairs of observed and synthetic seismograms the algorithm was designed specifically to accommodate synthetic seismograms produced from 3 d wavefield simulations which capture complex phases that do not necessarily exist in 1 d simulations or traditional traveltime curves relying on signal processing tools and several user tuned parameters the algorithm is able to include these new phases and to maximize the number of measurements made on each seismic record while avoiding seismic noise our motivation is to use the algorithm for iterative tomographic inversions in which the synthetic seismograms change from one iteration to the next hence automation is needed to handle the volume of measurements and to allow for an increasing number of windows at each model iteration the algorithm is sufficiently flexible to be adapted to many tomographic applications and seismological scenarios including those based on synthetics generated from 1 d models we illustrate the algorithm using data sets from three distinct regions the entire globe the japan subduction zone and southern california

alteration geochemistry of the nopal i uranium deposit sierra pena blanca mexico a natural analogue for a radioactive waste repository in volcanic tuffs natural analogues provide an approach to characterize and test the long term modelling of a repository performance this article presents geochemical information about the alteration conditions of the nopal i uranium deposit mexico an analogue for the proposed yucca mountain radioactive waste repository mineralization and hydrothermal alteration of volcanic tuffs are contemporaneous according to petrographic observations trace element geochemistry u th ree provides evidence for local mobilization of uranium under oxidizing conditions and further precipitation under reducing conditions o and hisotope geochemistry of kaolinite smectite opal and calcite suggests that argillic alteration proceeded at shallow depth with meteoric water at 25 75 c a low temperature context unusual for volcanic hosted uranium deposits this temperature range is compatible with some post closure evolution models of the proposed yucca mountain repository

steepest descent integration a novel method for computing wavefields radiated from borehole sources borehole sources which include chemical explosives air gun water gun piezoelectric transducers in the borehole generate seismic waves both in and outside the borehole modeling the wave field inside and outside the borehole is of key importance in acoustic logging crosshole tomography mining geophysics and deep sounding seismic for interpretation of amplitude information of real data and prediction of energy radiation pattern the classical methods for wavefield modeling inside the borehole such as real axis integration are challenged by highly oscillatory integrals outside the borehole we present a novel method called steepest descent integration sdi which evaluates the oscillatory wavenumber integration by numerically integrate along the steepest descent path the oscillation along the new integration path is extremely reduced the contribution of poles and branch cuts are added if they are located between the steepest descent path and the real axis the sdi is applicable to arbitrary freq

the complete synthesis of seismic crustal phases at regional distances using a new method to evaluate green s functions for elastic layered media we compute complete synthetic seismograms at regional distances for an earthquake in the earth crust we choose as source parameters the ones inferred for an earthquake in central france and compare the computed seismograms to the ones recorded at several short period stations of the french seismic network the major features of the records including complexity and duration are well reproduced by the synthetics lg waves which are the prominant phase are shown to be guided waves made up of sh and sv waves incident on the moho at angles of incidence more grazing than the critical angle and multiply reflected within the crust the length of the computed lg wave coda extends between group velocities of 3 5 and 2 8 km s and is in good agreement with the data

global anisotropic phase velocity maps for higher mode love and rayleigh waves summary it is well established that the earth s uppermost mantle is anisotropic but there are no clear observations of anisotropy in the deeper parts of the mantle surface waves are well suited to observe anisotropy since they carry information about both radial and azimuthal anisotropy fundamental mode surface waves for commonly used periods up to 200 s are sensitive to structure in the first few hundred kilometres and therefore do not provide information on anisotropy below higher mode surface waves have sensitivities that extend to and beyond the transition zone and should thus give insight about azimuthal anisotropy at greater depths we have measured higher mode love and rayleigh phase velocities using a model space search approach which provides us with consistent relative uncertainties from measurement to measurement and from mode to mode from these phase velocity measurements we constructed global anisotropic phase velocity maps prior to inversion we determine the optimum relative weighting for anisotropy we present global azimuthal phase velocity maps for higher mode rayleigh waves up to the sixth higher mode and love waves up to the fifth higher mode with corresponding average model uncertainties the anisotropy we derive is robust within the uncertainties for all modes given the ray theoretical sensitivity kernels of rayleigh and love wave modes the source of anisotropy is complex but mainly located in the asthenosphere and deeper our models show a good correspondence with other studies for the fundamental mode but we have been able to achieve higher resolution

alteration of uraninite from the nopal i deposit pen a blanca district chihuahua mexico compared to degradation of spent nuclear fuel in the proposed u s high level nuclear waste repository at yucca mountain nevada abstract at the nopal i uranium deposit primary uraninite nominally uo 2 x has altered almost completely to a suite of secondary uranyl minerals the deposit is located in a basin and range horst composed of welded silicic tuff uranium mineralization presently occurs in a chemically oxidizing and hydrologically unsaturated zone of the structural block these characteristics are similar to those of the proposed u s high level nuclear waste hlw repository at yucca mountain nevada petrographic analyses indicate that residual nopal i uraninite is fine grained 5 10 m and has a low trace element content average about 3 wt these characteristics compare well with spent nuclear fuel the oxidation and formation of secondary minerals from the uraninite have occurred in an environment dominated by components common in host rocks of the nopal i system e g si ca k na and h 2 o and also common to yucca mountain in contrast secondary phases in most other uranium deposits form from elements largely absent from spent fuel and from the yucca mountain environment e g pb p and v the oxidation of nopal i uraninite and the sequence of alteration products their intergrowths and morphologies are remarkably similar to those observed in reported corrosion experiments using spent fuel and unirradiated uo 2 under conditions intended to approximate those anticipated for the proposed yucca mountain repository the end products of these reported laboratory experiments and the natural alteration of nopal i uraninite are dominated by uranophane nominally ca uo 2 2 si 2 o 7 6h 2 o with lesser amounts of soddyite nominally uo 2 2 sio 4 2h 2 o and other uranyl minerals these similarities in reaction product occurrence developed despite the differences in time and physical chemical environment between yucca mountain approximate laboratory experiments and yucca mountain approximate uraninite alteration at nopal i suggesting that the results may reasonably represent phases likely to form during long term alteration of spent fuel in a yucca mountain repository from this analogy it may be concluded that the likely compositional ranges of dominant spent fuel alteration phases in the yucca mountain environment may be relatively limited and may be insensitive to small variations in system conditions

an inverse technique for retrieving higher mode phase velocity and mantle structure summary we present a new inverse method for retrieving the mantle structure using the fundamental and higher modes surface waves the fundamental mode is only sensitive to structures down to 400 500 km but higher modes have a depth resolution down to 1000 1500 km so they are well suited to the study of the transition zone between 400 and 1000 km depth a data set of seismograms corresponding to events all located in a small area and recorded at a single station is selected the inversion of the seismograms is divided into two steps first the difference between the real spectra and the sum of the higher modes synthetic spectra is inverted for retrieving the phase velocities of the first higher modes in a second step these phase velocities are inverted at depth in order to retrieve the average mantle structure between the receiver and the epicentral area this structure is modelled as a transversely isotropic medium with a vertical symmetry axis because of the non linearity of the problem it is necessary to iterate the procedure and to recalculate the earth eigenfunctions and the new synthetic spectra at each iteration numerical tests on synthetic data have been performed and they demonstrate that we have a good resolution at depth down to 1500 km some results obtained on real data recorded on geoscope network are also presented this method can now be applied systematically to real data

mobilization and redistribution of rees and thorium in a syenitic lateritic profile a mass balance study abstract ree th geochemistry and mineralogy have been studied in a lateritic profile derived from a syenite at akongo in sw cameroon ree and th mass balance calculations for the host rock minerals show that at least 70 of the lree s and 50 of the hrees are contained in allanite apatite titanite and epidote and at least 50 of the th is controlled by the same accessory minerals which represent about 2 wt of the unaltered syenite these accessory phases are destroyed during the first stages of weathering causing most of the rees and th to be rapidly released into the soil comparison of the variation in the zr ti and th content as a function of the apparent density of the different zones of the saprolite shows that th is the least mobile element the presence of secondary thorianite tho2 the etched surface on zircon grains and the presence of ti in secondary cerianite support this geochemical interpretation the concentration of thorium was therefore chosen as invariant relative to the concentration of the other elements especially the rees in mass balance calculations most of the rees are leached in the iron rich upper horizons loose nodular horizon iron crust and top of mottled clay horizon where the groundwater table moves saprolite and bottom of the mottled clay horizon the rees are fractionated and redistributed there is a juxtaposition of leached and accumulation zones with precipitation of lree aluminous hydrated phosphates this study supports the existence of two different cycles for the redistribution of elements in the soil 1 1 as dissolved ions in the saprolite horizon and 2 2 as individual particles in the upper part of the profile

a record of uranium series transport at nopal i sierra pena blanca mexico implications for natural uranium deposits and radioactive waste repositories abstract studies of uranium series u series disequilibria within and around ore deposits provide valuable information on the extent and timing of actinide mobility via mineral fluid interaction over a range of spatial and temporal scales such information is useful in studies of analogs of high level nuclear waste repositories as well as for mining and mineral extraction sites locations of previous nuclear weapons testing and legacy nuclear waste contamination in this study we present isotope dilution mass spectrometry u series measurements for fracture fill materials hematite goethite kaolinite calcite dolomite and quartz from one such analog the nopal i uranium ore deposit situated at pena blanca in the chihuahua region of northern mexico the ore deposit is located in fractured unsaturated volcanic tuff and fracture fill materials from surface fractures as well as fractures in a vertical drill core have been analyzed high uranium concentrations in the fracture fill materials between 12 and 7700 ppm indicate uranium mobility and transport from the deposit uranium concentrations generally decrease with horizontal distance away from the deposit but in this deposit there is no trend with depth below the surface isotopic activity ratios 238u 234u 230th 232th linear age trends and u th pa model ages indicate an actinide mobility evolution that can be characterized as complex and varied there is evidence of both open and closed system behavior for uranium depending on both sample and time scale the 234u 238u activity ratios indicate u mobility from 1 2 0 2 ma in the last 0 2 ma there is isotopic evidence for some u mobility but mostly u immobility in almost all cases the th pa radionuclides studied here have been immobile for the past 200 ka radium appears to have been recently 0 1 8 ka mobile due to ongoing fluid flow in the fractures overall the mainly closed system behavior for u th pa over the past 200 ka provides an indicator of the geochemical immobility of these actinides over time scales relevant for potential nuclear waste repositories situated in fractured unsaturated tuff

high resolution global phase velocity distributions we present global phase velocity distributions for fundamental mode love and rayleigh waves in the period range 40 to 150 seconds the models expressed in terms of spherical harmonic expansions up to degree and order 40 have beed derived from 28 479 love wave and 33 662 rayleigh wave measurements the measurements were made using an automatic procedure based on non linear waveform inversion we show that the results are characterized by lateral resolving radii between 500 and 850 km a significant reduction from previous work the improved global resolution is largely due to the inclusion of many more major arc measurements the power spectra of the models are much whiter than has previously been found the results show great similarity to the phase velocity distributions derived from the recent a priori model 3 smac in which the primary relevant features are the crustal thickness and crustal velocity distributions the cooling oceanic lithosphere and the thick 300km lithosphere of the continental cratons the results thus confirm these features differences for example in the strengths of the crust ridge and craton signatures should lead to refinement in the thermal and constitutive parameters upon which the a priori model depends

role of large particles in the transport of elements and organic compounds through the oceanic water column abstract during the past decade data from a variety of sources have been obtained which show conclusively that the relatively rare large particles sinking through the water column are responsible for the majority of the downward vertical mass flux in the sea this finding has important implications for understanding the transfer distribution and fate of elements and organic compounds in marine waters the large 100 m detrital particles responsible for vertical flux are primarily biogenic and range in size and composition from small discrete fecal pellets and plankton hard parts to large amorphous aggregates or snow which contain both organic and inorganic constituents depending on size shape and density these particles sink at rates ranging from 1000 m day 1 several methods have been developed for sampling these particles of which in situ sediment trapping has probably furnished the most comprehensive qualitative and quantitative information on the role large particles play in material transport flux studies have highlighted the importance of marine heterotrophs in packaging fine suspended particulate matter into large rapidly sinking particles which accelerate the movement of incorporated materials to depth large particle production via biological packaging is not restricted to the euphotic zone but can occur at all depths and information is now accruing on rates of production of large particles in the water column chemical analyses of sedimenting particles collected in sediment traps and those sampled by other means have allowed quantifying vertical fluxes and residence times of elements radionuclides and organic compounds natural and anthropogenic in various oceanic regimes pertinent studies dealing with the above aspects are reviewed and several areas for future research are suggested

automated multimode phase speed measurements for high resolution regional scale tomography application to north america summary a fully automated method for obtaining multimode phase speed measurements from a single seismogram has been developed and applied to a large data set of three component longperiod seismograms in north america constructing high resolution phase speed maps on a continental scale the method of our phase speed estimation is based on a fully non linear waveform inversion by yoshizawa kennett working with a global search method the neighbourhood algorithm the entire process of waveform fitting and the evaluation of the estimated phase speed have been fully automated employing several empirical quantitative measures assessing the quality of waveform fit and the relative contributions of each mode in a chosen time window the measured phase speed data undergo automatic screening for quality control comprising the threshold evaluation of their reliability and outlier detection and removal this new automated method has been applied to a large data set recorded at north american stations including the latest transportable stations of usarray using long period three component seismograms recorded during the past eight years we have successfully retrieved large numbers of regional surface wave paths including over 20000 paths for the fundamental mode rayleigh waves over a wide range of frequencies and over 10000 paths for the higher mode rayleigh as well as the fundamental mode love waves the consistentresultsoftheautomatedmeasurementproceduresuggestthatthemethodworkswell at regional distances allowing us to perform a high resolution mapping of multimode phase speeds in north america the results of the automated waveform analysis also indicate some intrinsic limitations in the higher mode phase speed measurements from a single seismogram particularly in the short period range mainly due to the overlapping of higher mode arrivals as well as coupling between mode branches despite such an innate difficulty in the higher mode dispersion measurements the automated method allows us to construct reliable multimode phase speed maps the current data set of ray paths is significantly biased towards the western half of north america resulting in non uniform horizontal resolution across the continent this issue will be resolved by the future migration of the usarray stations to cover the central and eastern united states the new automated method can be a useful tool for high resolution mapping of regional 3 d shear wave structure including possible anisotropy

ocean ecology life in an oceanic extreme scarce food supplies could hinder biological activity in the ocean s depths however measurements at mariana trench point to an unexpectedly active microbial community in the deepest seafloor setting on the planet

cerium anomalies in lateritic profiles the ree geochemistry and mineralogy have been studied in four lateritic profiles one derived from a syenite akongo sw cameroon the others being developed on a gneissic basement and located along a soil toposequence goyoum e cameroon there is a fractionation between lree and hree in the lateritic samples during weathering the weathered residual products being enriched in lree from la to eu and depleted in hree from gd to lu sampled waters are enriched in hree in relation to the syenite host rock a positive ce anomaly has been found systematically at the top of the saprolite beneath a zone of iron oxide accumulation in the laterite up to 2000 ppm ce may be present in the akongo profile cerianite ceo2 is present as very fine coatings in non ferruginous clayey domains primary ree bearing accessory minerals are weathered at the bottom of the profile specifically allanite and apatite are transformed into florencite and rhabdophane but these phases have no ce anomaly all the data are interpreted as the result of the following processes 1 1 ree leaching in a reducing environment 2 2 oxidation of ce3 to ce4 in an oxidizing environment 3 3 deposition of cerium as cerianite whereas the other ree remain in solution

surface wave array tomography in se tibet from ambient seismic noise and two station analysis i phase velocity maps summary empirical green s functions egfs between pairs of seismographs can be estimated from the time derivative of the long time cross correlation of ambient seismic noise these egfs reveal velocity dispersion at relatively short periods which can be used to resolve structures in the crust and uppermost mantle better than with traditional surface wave tomography we combine rayleigh wave dispersion estimates from egfs and from traditional two station ts analysis into a new approach to surface wave array tomography with data from dense receiver arrays we illustrate the methodology with continuous broad band recordings from a temporary seismographic network on the southeastern part of the tibetan plateau in sichuan and yunnan provinces sw china the egfs are robust under temporal changes in regional seismicity and the use of either ambient noise approximated by records without signal from events with magnitude mb 5 or 4 or surface wave coda produces similar results the egfs do not strongly depend on the presence of large earthquakes but they are not reciprocal for stations aligned in the n s direction this directionality reflects the paucity of seismicity to the north of the array using a far field representation of the surface wave green s function and an image transformation technique we infer from the egfs the rayleigh wave phase velocity dispersion in the period band from 10 30 s a classical ts approach is used to determine rayleigh wave phase velocity dispersion between 20 120 s together they constrain phase velocity variations for t 10 120 s which can be used to study the structure from the crust to the upper mantle beneath se tibet short and intermediate period 10 80 s phase velocities are prominently low suggesting that the crust and upper mantle beneath se tibet is characterized by slow shear wave propagation

mineralogical and stable isotope studies of kaolin deposits shallow epithermal systems of western sardinia italy large kaolin deposits hosted by miocene silicic pyroclastic rocks in northwestern sardinia represent hydrothermal alteration formed within 200 m of the miocene paleosurface boiling hydrothermal fluids ascended steeply dipping faults that are enveloped by altered rock the broadly stratiform kaolin deposits constitute advanced argillic alteration that was produced in a steam heated zone near the paleosurface overlying the deeper hydrothermal systems the deeper zones represent two distinct types of epithermal systems weakly acidic inferred low sulfidation systems at tresnuraghes and acidic high sulfidation systems at romana tresnuraghes is characterized at depth by chalcedony quartz barite veins within a 50 m wide zone of k feldspar quartz illite alteration and overlying local occurrences of chalcedony sinter which define the paleosurface kaolin deposits near the paleosurface are characterized by zonation outward and downward from an inner shallow zone of kaolinite 1t opal dickite alunite 20 m diam grains to an outer deeper kaolinite 1m montmorillonite cristobalite this zonation indicates formation by descending acidic fluids the system evolved from ascending weakly acidic or neutral fluids that boiled to produce h2s rich vapor which condensed and oxidized within the near surface vadose zone to form steam heated acid sulfate waters and kaolin alteration at romana veins at depth contain chalcedony or quartz and minor pyrite and are enclosed in up to 20 m wide zones of kaolinite 1t quartz alteration near hydrothermal vents along the paleosurface chalcedonic silica is enclosed within a zone of kaolinite 1t alunite 50 m diam grains quartz opal dickite cristobalite kaolin quarries near the paleosurface display outward and downward zoning to kaolinite 1t opal cristobalite and then to montmorillonite kaolinite 1t opal consistent with formation by descending low ph fluid the siliceous and advanced argillic alteration along steep conduits formed from acidic ascending magmatic hydrothermal fluids whereas the near surface kaolin formed from steam heated meteoric waters alteration mineral assemblages and stable isotope data provide evidence of the temperature and source of hydrothermal fluids barite from tresnuraghes average 18o 17 1 34s 18 8 one alunite sample from romana 18o 12 0 d 3 34s 16 7 and quartz from both localities 18o 15 9 22 0 formed in hydrothermal feeders source fluids were likely mixtures of meteoric water and minor magmatic fluid similar to other epithermal systems kaolinite dickite minerals from the kaolin deposits 18o 16 6 21 4 d 43 to 53 formed from steam heated meteoric water having d 20 per mil consistent with the presence of anomalous hg and fine grained na and fe poor alunite the laterally extensive kaolin deposits in sardinia and possibly similar deposits elsewhere in the world appear to represent the uppermost parts of large hydrothermal systems that may be prospects for gold at depth

retrieving lateral variations from surface wave dispersion curves surface wave analysis is usually applied as a 1d tool to estimate v s profiles here we evaluate the potential of surface wave analysis for the case of lateral variations lateral variations can be characterized by exploiting the data redundancy of the ground roll contained in multifold seismic data first an automatic processing procedure is applied that allows stacking dispersion curves obtained from different records and which retrieves experimental uncertainties this is carried out by sliding a window along a seismic line to obtain an ensemble of dispersion curves associated to a series of spatial coordinates then a laterally constrained inversion algorithm is adopted to handle 2d effects although a 1d model has been assumed for the forward problem solution we have conducted different tests on three synthetic data sets to evaluate the effects of the processing parameters and of the constraints on the inversion results the same procedure applied to the synthetic data was then tested on a field case both the synthetic and field data show that the proposed approach allows smooth lateral variations to be properly retrieved and that the introduction of lateral constraints improves the final result compared to individual inversions

broadband ground motion simulation within the city of duzce turkey and building response simulation in areas with significant seismic activity and insufficient seismic networks simulated ground motions are required for both seismic hazard and engineering analyses one important task is evaluating the efficiency of the simulated records in building response estimation in this study a hybrid ground motion simulation framework is presented to obtain broadband ground motion time histories of a past major earthquake in duzce turkey the hybrid ground motion simulation framework presented herein is a combination of a discrete wavenumber finite element method for simulating low frequencies and a stochastic finite fault method for the higher frequencies the proposed technique is first validated by the simulation of the 12 november 1999 duzce earthquake m text w 7 1 which occurred in the north anatolian fault zone turkey peak simulated ground motions at selected nodes are then compared against ground motion prediction equations derived with global and local data sets next the spatial distribution of simulated peak ground motion intensities are obtained in the region and compared with the observed damage distribution results demonstrate that the earthquake is simulated effectively despite the limitations in number of stations and velocity models finally to evaluate the simulated records in building response estimation nonlinear time history analyses of three reinforced concrete multi degree of freedom structures are performed with real and simulated records of the 1999 duzce earthquake in the opensees platform the results reveal that reasonable predictions can be made regarding the dynamic response of structures using the records simulated with the approach presented herein

x ray imaging of uranium in individual fluid inclusions the spatial distribution of major k ca mn fe and trace elements ti cr cu as br rb sr zr pb th u were determined in individual fluid inclusions from quartz veins of the streltsov uranium deposit russia using synchrotron radiation x ray fluorescence sxrf the analyses were performed on the beamline id 22 micro fid fluorescence imaging diffraction of the european synchrotron research facility esrf grenoble france fluorescence x ray maps of single fluid inclusions show a relatively homogeneous distribution of most elements throughout the inclusion whereas fe and to a lesser extent sr display highly localized count rates this observation argues for the presence of minute optically invisible compounds that are precipitated inside the inclusion simple model calculations indicate that relatively diluted solutions 10 100 ppm u trapped at geologically relevant temperatures e g 250 c would precipitate submicron sized particles these particles would be highly reactive to the photon flux but not necessarily visible under the microscope these results indicate that third generation synchrotron light source can be a powerful technique to study the physical processes undergone by the fluid when combined with chemical data this technique can help to clarify fluid transport properties in natural systems

assessment of global phase velocity models summary we construct new love and rayleigh wave phase velocity models based on measurements made from an aspherical starting model and strict data quality control derived from cluster analyses these new models are in good agreement with previous ones and the question arises whether the slight changes show an improved capacity to explain the data to this effect we propose an objective method to compare different phase velocity models published in recent literature the method is based on comparing calculated synthetics to raw seismograms we find a reassuring convergence between all the models we tested at the longest periods and more scatter at the shorter periods at 40 s the different models show gains of up to 3 5 cycles over prem generally the higher the gain over prem the smaller the period considered which confirms that the earth s heterogeneity is strongest in the uppermost parts of the earth apart from assessing different models against each other our method gives an estimate comparable to cluster analyses of the underlying data errors that went into the construction of the models themselves moreover ray coverage is still far from perfect for constructing phase velocity models as a result we find that without precaution degree zero is biased through spectral leakage by 0 1 to 0 2 per cent with respect to prem the earliest information concerning the earth s 3 d structure came from surface waves when tams 1921 noticed clear velocity differences for waves propagating along continental versus oceanic paths gutenberg 1924 attempted an explanation of such differences in terms of regional variations in crustal structure when he noticed that short period surface waves are more sensitive to crustal structure than long period ones this led the way to intensive studies both theoretical and observational to link dispersive properties of surface waves to the internal structure of the earth the first regional models of the earth s dispersive properties of crust and upper mantle are summarized in papers by brune 1969 and dorman 1969 respectively with the start of digital recording of seismograms in the late

the relative density to shear velocity scaling in the uppermost mantle we perform inversions of gravity data geopotential model egm96 and seismic tomography model s16rlbm for the scaling factor which relates relative density anomalies to relative s wave velocity anomalies the gravity data and tomographic model are anti correlated below continents down to a depth of z 200 km this anti correlation is not present below oceans except for smoothness which is controlled by a damping factor no a priori information is added to the inversion data are filtered between degrees 11 and 16 of the spherical harmonic expansion this spectral window is well suited for the study of intermediate size 2000 4000 km anomalies in the uppermost mantle calculations are made separately for sub continental and sub oceanic mantle the sub continental and sub oceanic scaling factors are significantly different at depths shallower than 260 km in both cases the magnitude of is around 0 05 the sub continental scaling factor has a positive root down to z 220 km whereas the sub oceanic scaling factor yields positive values down to z 140 km only at depth shallower than 350 km models of do not depend on the damping factor or the viscosity model at depths greater than 350 km the resolution of z decreases significantly and low degrees 2 4 add information from large scale anomalies and from the lower mantle as a result the shape and values of for 2 16 and 11 16 are significantly different at depths greater than 350 km a possible explanation of the discrepancies between the sub continental and sub oceanic scaling factor is that intermediate scale anomalies are more important in the continental uppermost mantle than in the oceanic uppermost mantle 2001 elsevier science b v all rights reserved

evidence for nanocrystals of vorlanite a rare uranate mineral in the nopal i low temperature uranium deposit sierra pena blanca mexico the occurrence of vorlanite cubic cauo4 is reported in the nopal i uranium deposit sierra pena blanca mexico this is the first time this rare calcium uranate has been found displaying a cubic morphology in agreement with its crystal structure vorlanite occurs as nanoscale crystals embedded in u bearing opal with a ca u ratio of 1 association with opal suggests that vorlanite formed at nopal during late stage u mobilization under oxidizing conditions and low 50 c temperature the presence of nanoscale uranate crystals in an environment largely dominated by uranyl silicates indicates that uranates may play a role in uranium scavenging at low temperature in addition the occurrence of vorlanite in the crystal shape consistent with its structure provides unique information on its conditions of formation

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

exceptional silica speleothems in a volcanic cave a unique example of silicification and sub aquatic opaline stromatolite formation terceira azores this research was funded by the spanish ministry of economy and competitiveness project cgl2011 27826 co2 02

radially anisotropic 3 d shear wave structure of the australian lithosphere and asthenosphere from multi mode surface waves abstract a new radially anisotropic shear wave speed model for the australasian region is constructed from multi mode phase dispersion of love and rayleigh waves an automated waveform fitting technique based on a global optimization with the neighbourhood algorithm allows the exploitation of large numbers of three component broad band seismograms to extract path specific dispersion curves covering the entire continent a 3 d shear wave model is constructed including radial anisotropy from a set of multi mode phase speed maps for both love and rayleigh waves these maps are derived from an iterative inversion scheme incorporating the effects of ray path bending due to lateral heterogeneity as well as the finite frequency of the surface waves for each mode the new s wave speed model exhibits major tectonic features of this region that are in good agreement with earlier shear wave models derived primarily from rayleigh waves the lateral variations of depth and thickness of the lithosphere asthenosphere transition lat are estimated from the isotropic voigt average s wave speed model and its vertical gradient which reveals correlations between the lateral variations of the lat and radial anisotropy the thickness of the lat is very large beneath the archean cratons in western australia whereas that in south australia is thinner the radial anisotropy model shows faster sh wave speed than sv beneath eastern australia and the coral sea at the lithospheric depth the faster sh anomaly in the lithosphere is also seen in the suture zone between the three cratonic blocks of australia one of the most conspicuous features of fast sh anisotropy is found in the asthenosphere beneath the central australia suggesting anisotropy induced by shear flow in the asthenosphere beneath the fast drifting australian continent

an efficient method for computing green s functions for a layered half space at large epicentral distances nowadays with the dramatic increase in computational ability the dis crete wavenumber integration method dwim see e g bouchon and aki 1977 bouchon 1979 1981 has been one of the most favorable techniques of computing the synthetic seismograms for a layered half space because of its simplicity accuracy and fair efficiency for some cases particularly for the case of the near field however it becomes less efficient for the case of far field that is at large epicentral distances and the larger the epicentral distance is the less efficient dwim will be in this study we propose an efficient numerical wavenumber integration method the self adaptive filon s integration method safim to compute efficiently the dynamic green s functions for a layered half space at large epicentral distances this new integration technique is build upon the particular fifth order filon s integration scheme apsel 1979 apsel and luco 1983 and the principle of the self adaptive simpson inte gration technique by using numerical examples we demonstrate that safim is not only accurate but also very efficient for large epicentral distances according to our study we find that at a relatively short epicentral distance r 500 km the classical dwim is more efficient than safim at a medium range of epicentral distance 500 kmr 1200 km both methods have similar efficiency at large epicentral dis tance r 1200 km however safim is significantly more efficient than dwim and the larger the epicentral distance is the more efficient safim will be for in stance when r 2000 km safim only needs about 1 3 of the computation time of dwim therefore this new integration method is expected to be very useful in com puting synthetic seismograms at large epicentral distances

geology geochemistry and origin of volcanic rock hosted uranium deposits in northwestern nevada and southeastern oregon usa abstract northwestern nevada and southeastern oregon have the largest uranium u deposits in tertiary volcanic rocks in the us most deposits are in or adjacent to calderas or rhyolite lava dome fields and are hydrothermal almost all are associated with rhyolites that have high primary u concentrations 9 to 20 ppm but the rhyolites range from peralkaline to peraluminous caldera related occurrences are hosted by peralkaline rocks in the mcdermitt and virgin valley calderas at mcdermitt major deposits are along or just inboard of the southwestern kings river and northern ring fractures bretz opalite of the caldera complex the kings river deposits are strongly enriched in trace elements associated with epithermal precious metal deposits e g as au ag mo and sb much of the u occurs as hydrothermal uraniferous zircon and whole rock samples contain as much as 5 zr gangue minerals include quartz adularia fluorite and numerous sulfides 40 ar 39 ar dating of adjacent volcanic rocks and adularia indicates that mineralization was contemporaneous with igneous activity the bretz opalite deposits which include the large aurora resource 7 5 106 kg u3o8 are less enriched in epithermal trace elements and contain uraninite coffinite chalcedony opal and numerous sulfides at virgin valley deposits are mostly in tuffaceous sediments adjacent to ring fracture rhyolites trace element enrichment is minor u is hexavalent in all identified u minerals and associated phases include opal organic material and pyrite deposits in the lakeview u district oregon are hosted by weakly peraluminous rhyolite domes and tuffs and are highly enriched in epithermal trace elements the mineral assemblage includes coffinite opal and numerous sulfides minor u occurrences at buff peak nevada the newly recognized westernmost topaz peraluminous rhyolite in the us are also trace element enriched gangue minerals include quartz adularia and sulfides on the basis of their geologic setting geochemistry age and mineralogy the mcdermitt lakeview and buff peak deposits are hydrothermal sparse published fluid inclusion data indicate temperatures between 200 c and 330 c virgin valley deposits most likely are hydrothermal minor deposits in outflow ash flow tuffs are distant from any intrusive heat source and probably formed from low temperature groundwater

surface wave tomography for the pacific ocean incorporating seafloor seismic observations and plate thermal evolution abstract using broadband seismic waveforms recorded on the seafloor by more than 200 broadband ocean bottom seismometers as well as those on land we measured the phase speed dispersions of love and rayleigh waves up to the 4th higher mode to determine the three dimensional radially anisotropic shear wave speed structure in the upper mantle beneath the pacific ocean the fastest anomalies at depths shallower than 100 km were located beneath southeast of the shatsky rise and strong radial anisotropy was located in the central pacific at depths of 100 200 km the isotropic shear wave speed structures showed age dependence from the age bin averaged shear wave speed profiles and a half space cooling model we estimated the thermo speed relationship for the pacific plate to construct a reference age dependent shear wave speed model which was further used as an initial model for tomography iteration deviation maps in the pacific ocean from the reference model indicated that large negative residuals which may be due to partial melting anelasticity and or added heat from mantle plumes were located along the ridges and beneath hotspots and that large positive residuals were found beneath the northwestern pacific ocean the use of an age dependent reference model as well as the incorporation of obs data greatly improves the accuracy of local phase speed estimates in tomography as evident from a direct comparison with in situ array measurements

uranium rich opal from the nopal i uranium deposit pena blanca mexico evidence for the uptake and retardation of radionuclides abstract the nopal i uranium deposit of the sierra pena blanca mexico has been the focus of numerous studies because of its economic importance and its use as a natural analog for nuclear waste disposal in volcanic tuff secondary uranyl minerals such as uranophane ca uo2 sio3oh 2 h2o 5 and weeksite k na 2 uo2 2 si5o13 h2o 3 occur in the vadose zone of the deposit and are overgrown by silica glaze these glazes consist mainly of opal a which contains small particles of uraninite uo2 and weeksite close to a fault between brecciated volcanic rocks and welded tuff a greenish silica glaze coats the altered breccia yellow silica glazes from the center of the breccia pipe and from the high grade pile coat uranyl silicates predominantly uranophane and weeksite all silica glazes are strongly zoned with respect to u and ca and the distribution of these elements indicates curved features and spherical particles inside the coatings the concentrations of u and ca correlate in the different zones and both elements inversely correlate with the concentration of si zones within the silica glazes contain u and ca in a 1 1 ratio with maximum concentrations of 0 08 and 0 15 at for the greenish and yellow glazes respectively suggesting trapping of either ca1u1 aqueous species or particles in the colloidal silica x ray photoelectron spectroscopy xps fourier transform infra red spectroscopy ftir and oxygen isotope ratios measured by secondary ion mass spectrometry sims indicate higher u6 u4 ratios higher proportions of si oh groups and lower 18o values for the greenish silica glaze than for the yellow silica glaze these differences in composition reflect increasing brecciation porosity and permeability from the center of the breccia pipe yellow silica glaze toward the fault green silica glaze where the seepage of meteoric water and eh are higher

uranium transport through fractured silicic tuff and relative retention in areas with distinct fracture characteristics abstract the nopal i uranium u deposit in the pefia blanca district chihuahua mexico has been identified as analogous in some regards to the candidate u s high level waste hlw repository at yucca mountain nevada uranium transport at the nopal i deposit has been studied to investigate mechanisms by which hlw components could be transported through silicic tuff over long time periods this investigation focused on approximately 1400 m2 of essentially continuous bedrock outcrop spanning the nopal i deposit and surrounding host tuff data collected document i the distributions of u within and around the nopal i deposit ii the distribution and characteristics of the fracture network within and surrounding the deposit and iii the transport of u away from the deposit mainly along fracture paths uranium series isotopic measurements indicate mobilization of u along the margin of the deposit within the last 1 ma and significant u transport at about 54 ka transport of u away from the nopal i deposit along a few relatively continuous mesofractures achieved maximum distances at least 20 times greater than transport through the general fracture network composed of thousands of less continuous microfractures within and surrounding the deposit uranium transport away from the deposit appears to be largely independent of variations in the general fracture network pattern transport of u away from individual micro and meso fractures into homogeneous unfractured tuff matrix appears limited to distances less than 1 mm at the nopal i deposit matrix diffusion does not appear to have been an important factor for retardation of u this analysis suggests a ranking for u retention i microfracture network retention mesofracture retention and ii individual microfracture retention matrix retention

uranium bearing opals products of u mobilization diffusion and transformation processes understanding the retention mechanism of u by amorphous silica i e opal in the environment is of great importance to nuclear waste disposal because opals can retain u for millions of years uraniferous opals from spor mountain and the thomas range utah u s a are examined in terms of their mineralogical chemical and isotopic compositions uranium rich zones composed of most likely vorlanite cauo 4 occur in fibrous opal ct termed lussatite along the interface of the phase with microcrystalline quartz red to black colored precipitates of vorlanite also occur in the interstices between fibers and grains in lussatite and massy opals respectively the high abundance of vorlanite in certain growth zones can be explained by the diffusion of ca and u along boundaries of layers grains and fibers and by the release of ca and u through the transformation of opal a into opal ct and from opal ct into microcrystalline quartz similar o isotope compositions of opal ct and associated microcrystalline quartz indicate that crystallization processes and deposition of subsequent layers of opal occurred from fluids of similar origin and t differences in the isotope and chemical composition between uraniferous opals microcrystalline quartz the sio 2 polymorph moganite and pyrolusite indicate the past occurrence of various alteration processes involving fluids of different composition and t the results of this study indicate that assemblages of opal and microcrystalline quartz can retain u for millions of years as long as confined pore spaces between different generations of opal and quartz or between growth features of opal provide space for the nucleation and adsorption of u bearing phases and species

global love wave overtone measurements 1 love wave phase velocities for fundamental and higher modes are difficult to measure because the different modes cannot easily be separated following yoshizawa and kennett 2002 we generate suites of path specific onedimensional shear wave velocity profiles using the neighbourhood algorithm of sambridge 1999a from this family of o 10 4 models both fundamental and higher mode phase velocities with mutually consistent uncertainties are calculated we have fully automated the method and analysed over forty thousand love wave seismograms from the gdsn and geoscope global networks from 1994 2004 our phase velocity measurements agree remarkably well with previous studies but we have been able to enlarge the available dataset dramatically we present global love wave phase velocity maps up to the fifth overtone with unprecedented resolution due to the improved path coverage comparing these maps to existing tomographic models we discern evidence of significant anisotropy inthe lower mantlearound a depth of 1000 km in the pacific citation visser k s lebedev j trampert and b l n kennett 2007 global love wave overtone measurements geophys res lett 34 l03302

study of two alteration systems as natural analogues for radionuclide release and migration abstract u deposit hosted in hydrothermally altered tuffs in mexico together with weathering profiles from cameroon were studied as natural analogues of radionuclide release and migration using petrological and spectroscopic methods infrared and electron paramagnetic resonance we have distinguished successive secondary mineral parageneses and the behaviour of radionuclides in the u deposit the mineral parageneses show that uranium migration is mainly controlled by the redox potential and silica activity of the altering solutions the high silica content of the solutions is caused by the intense alteration of volcanic rocks two types of secondary clay mineral parageneses are evidenced a kaolinization intense where uranium is accumulated in the welded tuffs and a smectitization mainly developed in the underlying weakly welded tuffs several types of kaolinite have been defined according to their genesis fillings in fissures and feldspar pseudomorphs their location relative to a breccia pipe where uranium has accumulated core and rim of the pipe surrounding rhyolitic tuffs and particle morphology structural order and substitutional fecontent it is shown that the variations of the concentration of paramagnetic defect centres always more than ten times as important than those measured in weathering kaolinites are only correlated to the location of the kaolinites the highest values correspond to the breccia pipe kaolinites e g kaolinites located in the uranium accumulation zones moreover one or two main defects centres are detected depending on the intimate association of kaolinites with uranium bearing minerals besides in weathering kaolinites from u depleted laterites defect centre concentrations are correlated to the total fe203 content in bulk samples this means that the defect centre acts as a memory of the travel of uranium when this element was sorbed onto iron gels in the first stage of weathering it is concluded that paramagnetic defect centres in kaolinites might allow an efficient fingerprint of successive irradiations in the natural analogues under study and could be an useful tool to control radionuclides migration through kaolinite containing clayey materials such as those used for waste repository a better understanding of radiation efficiency as well as accurate dose ratekaolinite containing clayey materials such as those used for waste reposit estimation are needed for a quantitative tracing of the migration ofa better understanding of radiation efficiency as well as accurate dose ratekaolin radionuclide elements with this aim a simulation has been undertaken withestimation are needed for a quantitative tracing of the migration of various radiations sources we have determined for each irradiation the parameters of the paramagnetic centres created in order to understand the way they are forming the knowledge of the parameters governing the formation and the stability of the radiation centres in kaolinites allow to use this mineral as a natural dosimeter

strong ground motion simulation of the 6 april 2009 l aquila italy earthquake on 6 april 2009 an earthquake of mw 6 13 herrmann et al 2011 occurred in central italy close to the town of l aquila although the earthquake is considered to be a moderate size event it caused extensive damage to the surround ing area the earthquake is identified with significant directivity effects high amplitude short duration motions are observed at the stations that are oriented along the rupture direction whereas low amplitude long duration motions are observed at the stations oriented in the direction opposite to the rupture the complex nature of the earthquake combined with its damage potential brings the need for studies that assess the seismological characteristics of the 2009 l aquila mainshock in this study we present the strong ground motion simulation of this particular earthquake using a stochastic finite fault model with a dynamic corner frequency ap proach for modeling the resulting ground motions we choose two finite fault source models that take into account the source complexity of the l aquila mainshock in order to test the sensitivity of ground motion parameters to the seismic wave attenua tion parameters we use two different attenuation models obtained in the study region using weak motion and strong motion databases comparisons are made between the attenuation of synthetics and ground motion prediction equations gmpes synthetic ground motions are further compared with the observed ones in terms of fourier amplitude and response spectra at 21 strong ground motion stations that recorded the mainshock within an epicentral distance of 100 km the spatial distribution of shaking intensity obtained from the did you feel it project and site survey results are compared with the spatial distributions of simulated peak ground motion intensity parameters our results show that despite the limitations of the method in simulating the directivity effects the stochastic finite fault model seems an effective and fast tool to simulate the high frequency portion of ground motions

global mantle tomography progress status in the past 10 years abstract we review the present status of global mantle tomography and discuss two main classes of models that have been developed in the past 10 years p velocity models based on large datasets of travel times from the international seismological centre bulletins often referred to as high resolution models and s velocity models based on a combination of surface wave and hand picked body wave travel times or waveforms referred to as long wavelength models we discuss their respective strengths and weaknesses as well as progress in the resolution of other physical parameters such as anisotropy anelasticity density and bulk sound velocity using tomographic approaches we present the view that future improvements in global seismic tomography require the utilization of the rich information contained in complete broadband seismic waveforms this is presently within our reach owing to theoretical progress as well as the increase in computational power in recent years

recent sediment transport and deposition in the nazare canyon portuguese continental margin processes pathways and fluxes of sediment transport and deposition in the nazare submarine canyon portuguese continental margin were investigated by water column profiling of suspended particulate matter recording of near bottom currents and suspended particulate matter fluxes with benthic landers and by analysis of surface sediment cores the results show that fine grained suspended sediment from the adjacent shelf is captured in the upper canyon and actively transported through the canyon to the abyssal plain under influence of tidal currents and intermittent sediment gravity flows tidal currents are actively resuspending and transporting sediment in the upper to middle canyon as reflected by high concentration of suspended particles in bottom waters high horizontal and vertical sediment fluxes in the bottom water layer and high sediment accumulation rate on the seabed diminishing strength of tidal currents leads to focussed sediment deposition in the middle canyon further transport of sediments toward the lower canyon takes place predominantly by sediment gravity flows occurring on yearly or longer timescale turbidity currents strong enough to transport sand sized material to the lower canyon occur only on centennial or longer timescales

three dimensional shear wave structure beneath the philippine sea from land and ocean bottom broadband seismograms 1 we obtained three dimensional 3 d shear wave speed structure beneath the philippine sea and the surrounding region from seismograms recorded by land based and long term broadband ocean bottom seismographic stations the ocean bottom data gave us a better station coverage to obtain a higher spatial resolution about 300 400 km in the philippine sea than in previous studies we employed a new technique of surface wave tomography in which multimode phase speeds are measured and inverted for a 3 d shear wave speed structure by incorporating the effects of finite frequency and ray bending there is a sharp speed contrast along the izu bonin mariana trench across which the philippine sea side has a significantly slower upper mantle than the pacific ocean side in the upper 120 km the shear wave speed structure is well correlated with the age of the provinces at depths greater than 160 km the pattern is dominated by fast anomalies of the subducted slabs of the pacific plate and two slow anomalies to the south of the daito ridge and in the southernmost part of the philippine sea

luminescence of uranium bearing opals origin and use as a ph record abstract fluorescence of minerals has been long used for u exploration it is proposed here that opal fluorescence can be used as a probe of the ph of the formation solution bringing constraints for modeling u speciation and sequestration at the earth s surface we present a study of fluorescence spectroscopy of u in opals resulting from low temperature 29 c alteration of mineralized rhyolitic lavas nopal i u deposit sierra pena blanca mexico these opals show green fluorescence with a concentric distribution at microscopic scale which is unambiguously assigned to uranyl groups oxidized form of u spectra appear typical of uranyl in opal as reported in literature for other localities according to peak positions when considering also the lifetime of fluorescence spectra with time resolved laser fluorescence spectroscopy fingerprinting indicates that uranyl occurs either as phosphate or hydroxo polynuclear complexes trapped onto the opal internal surface data are indicative of a ph of opal formation around 8 as derived from both conditions of laboratory experiments and reference to calculated diagrams of speciation this ph value is consistent with the nopal geological formations that were potentially in contact with the aquifer involved in the hydrothermal process in addition the microscopic zoning of u suggests that the speciation has been stable since opal formation more than 50 ka ago which allows the record of ph that prevailed at that time

structural and biological control of the cenozoic epithermal uranium concentrations from the sierra pena blanca mexico epithermal uranium deposits of the sierra pena blanca are classic examples of volcanic hosted deposits and have been used as natural analogs for radionuclide migra tion in volcanic settings we present a new genetic model that incorporates both geochemical and tectonic features of these deposits including one of the few documented cases of a geochemical signature of biogenic reducing conditions favoring uranium mineralization in an epithermal deposit four tectono magmatic faulting events affected the volcanic pile uranium occurrences are associated with breccia zones at the intersection of fault systems periodic reactivation of these structures associated with basin and range and rio grande tectonic events resulted in the mobilization of u and other elements by meteoric fluids heated by geothermal activity focused along breccia zones these fluids precipi tated under reducing conditions several generations of pyrite and uraninite together with kaolinite oxygen isotopic data indicate a low formation temperature of uraninite 45 55 c for the uraninite from the ore body and 20 c for late uraninite hosted by the underlying conglomerate there is geochemical evidence for biological activity being at the origin of these reducing conditions as shown by low 34 s values 24 5 in pyrites and the presence of low 13 c 24 values in microbial patches intimately associated with uraninite these data show that tectonic activity cou pled with microbial activity can play a major role in the formation of epithermal uranium deposits in unusual near surface environments

high rates of microbial carbon turnover in sediments in the deepest oceanic trench on earth microbes regulate the decomposition of organic matter in marine sediments measurements at the deepest oceanic site on earth reveal high rates of microbial activity potentially fuelled by the deposition of organic matter microbes control the decomposition of organic matter inmarine sediments decomposition in turn contributes to oceanic nutrient regeneration and influences the preservation of organic carbon1 generally rates of benthic decomposition decline with increasing water depth although given the vast extent of the abyss deep sea sediments are quantitatively important for the global carbon cycle2 3 however the deepest regions of the ocean have remained virtually unexplored4 here we present observations of microbial activity in sediments at challenger deep in the mariana trench in the central west pacific which at almost 11 000 m depth represents the deepest oceanic site on earth we used an autonomous micro profiling system to assess benthic oxygen consumption rates we show that although the presence of macrofauna is restricted at challenger deep rates of biological consumption of oxygen are high exceeding rates at a nearby 6 000 m deep site by a factor of two consistently analyses of sediments collected from the two sites reveal higher concentrations of microbial cells at challenger deep furthermore analyses of sediment 210pb profiles reveal relatively high sediment deposition in the trench we conclude that the elevated deposition of organic matter at challenger deep maintains intensified microbial activity at the extreme pressures that characterize this environment

asthenospheric flow and origin of volcanism in the baikal rift area the origin of low volume hotspot like volcanism often observed in continental rift areas is debated as is the nature of the flow in the mantle beneath in this paper we assemble seismic constraints on the mantle flow below the baikal rift zone we combine new evidence from upper mantle tomography and from a radially anisotropic shear velocity profile measured beneath and se of the rift with published shear wave splitting constraints on azimuthal anisotropy fast directions of azimuthal anisotropy are perpendicular to the rift on both of its sides stable siberian platform lithosphere on the northern side extends down to 200 km on the southern side the lithosphere is only 60 70 km thick this asymmetry with the thick cratonic root forming a barrier to convective flow inhibits a mid ocean ridge like flow pattern the radially anisotropic profile yields evidence for horizontal flow in the upper asthenosphere 60 100 km se of the rift but no evidence for vertical flow these results are consistent with horizontal asthenospheric flow nw to se perpendicular to the rift from beneath the thick siberian towards the thin baikal mongolian lithosphere when asthenosphere ascends from the 200 km depth beneath the craton to shallower depths beneath the rift decompression melting of embedded veins of enriched rock can produce the hotspot like basaltic volcanism observed the occurrence of such veins of enriched mantle in sub cratonic asthenosphere has been predicted by geochemical mantle models we propose that sub horizontal asthenospheric flow from beneath cratons is a common cause for hotspot like volcanism in continental rift zones

volcanogenic uranium mineralizations in the sierra pena blanca district chihuahua mexico three genetic models the sierra pena bianca district is a good example of uranium deposits related to volcanic rocks which are here considered to be both the source of the uranium and the host rocks for its deposition the mineralization occurs mainly in the lower units of a cenozoic volcanic pile the nopal and escuadra rhyolites that overlie a mesozoic calcareous basement three genetic types of mineralization have been identified 1 a hydrothermal type illustrated by the nopal 1 deposit the primary mineralization relics of a pitchblende pyrite association are observed and the associated kaolinization of the rock are related to the circulation of hydrothermal fluids in breccias and fault systems the present day mineralization consists of mainly u super 6 minerals uranophane weeksite etc produced during later stages under oxidized conditions 2 a mixed supergene exhalative type exemplified by the las margaritas deposit the u mo minerals precipitated due to the mixing of oxidized u enriched ground waters with reduced h 2 s rich fluids in a tectonic valley 3 a supergene type reflected by the puerto 3 deposit the u super 6 mineralization uranophane is located between two impermeable layers and has a roll shape the precipitation of this u super 6 silicate with kaolinite and quartz is due to an sio 2 enrichment of the solutions at low temperature

global shear speed structure of the upper mantle and transition zone s u m m a r y the rapid expansion of broad band seismic networks over the last decade has paved the way for a new generation of global tomographic models significantly improved resolution of global upper mantle and crustal structure can now be achieved provided that structural information is extracted effectively from both surface and body waves and that the effects of errors in the data are controlled and minimized here we present a new global vertically polarized shear speed model that yields considerable improvements in resolution compared to previous ones for a variety of features in the upper mantle and crust the model sl2013sv is constrained by an unprecedentedly large set of waveform fits 3 4 of a million broad band seismograms computed in seismogram dependent frequency bands up to a maximum period range of 11 450 s automated multimode inversion of surface and s wave forms was used to extract a set of linear equations with uncorrelated uncertainties from each seismogram the equations described perturbations in elastic structure within approximate sensitivity volumes between sources and receivers going beyond ray theory we calculated the phase of every mode at every frequency and its derivative with respect to sand p velocity perturbations by integration over a sensitivity area in a 3 d reference model the normally small perturbations of the 3 d model required to fit the waveforms were then linearized using these accurate derivatives the equations yielded by the waveform inversion of all the seismograms were simultaneously inverted for a 3 d model of shear and compressional speeds and azimuthal anisotropy within the crust and upper mantle elaborate outlier analysis was used to control the propagation of errors in the data source parameters timing at the stations etc the selection of only the most mutually consistent equations exploited the data redundancy provided by our data set and strongly reduced the effect of the errors increasing the resolution of the imaging our new shear speed model is parametrized on a triangular grid with a 280 km spacing in well sampled continental domains lateral resolution approaches or exceeds that of regionalscale studies the close match of known surface expressions of deep structure with the distribution of anomalies in the model provides a useful benchmark in oceanic regions spreading ridges are very well resolved with narrow anomalies in the shallow mantle closely confined near the ridge axis and those deeper down to 100 120 km showing variability in their width and location with respect to the ridge major subduction zones worldwide are well captured extending from shallow depths down to the transition zone the large size of our waveform fit data set also provides a strong statistical foundation to re examine the validity field of the jwkb approximation and surface wave ray theory our analysis shows that the approximations are likely to be valid within certain time frequency portions of most seismograms with high signal to noise ratios and these portions can be identified using a set of consistent criteria that we apply in the course of waveform fitting

oxygen isotope geochemistry of hydrothermally altered synmetamorphic granitic rocks from south central maine usa hydrothermally altered mesozonal synmetamorphic granitic rocks from maine have whole rock 18o smow values 10 7 to 13 8 constituent quartz feldspar and muscovite have 18o in the range 12 4 to 15 2 10 0 to 13 2 and 11 1 to 12 0 respectively mean values of q f 18oquartz 18ofeldspar 2 4 and q m 18oquartz 18omuscovite 3 3 are remarkably uniform standard deviations of both are 0 2 measured q f and q m values demonstrate that the isotopic compositions of the minerals are altered from primary magmatic 18o values but that the minerals closely approached oxygen isotope exchange equilibrium at subsolidus temperatures analyzed muscovites have d smow values in the range 65 to 82 feldspars in the granitic rocks are mineralogically altered to either a muscovite calcite b muscovite calcite epidote c muscovite epidote or d muscovite only a consistent relation exists between the assemblage of secondary minerals and the oxygen isotope composition of whole rocks quartz and feldspar rocks with assemblage a have whole rock 18o 12 1 and contain quartz and feldspar with 18o 13 8 and 11 4 respectively rocks with assemblages b c and d have whole rock 18o 11 4 and contain quartz and feldspar with 18o 13 1 and 11 0 respectively the correlation suggests that the mineralogical alteration of the rocks was closely coupled to their isotopic alteration three mineral thermometers in altered granite suggest that the hydrothermal event occurred in the temperature range 400 150 c 100 150 c below the peak metamorphic temperature inferred for country rocks immediately adjacent to the plutons calculations of mineral fluid equilibria indicate that samples with assemblage a coexisted during the event with co2 h2o fluids of text x text co text 2 0 03 0 13 and 18o 10 8 to 12 2 while samples with assemblages b c or d coexisted with fluids of text x text co text 2 leqslant 0 03 and 18o 9 4 to 10 1 compositional variations of the hydrothermal fluids were highly correlated fluids enriched in co2 were also enriched in 18o because co2 was added to the granites during hydrothermal alteration and because fluids enriched in co2 were enriched in 18o some or all of the variation in 18o of altered granites may have been caused by addition of 18o to the rocks during the hydrothermal event the source of both the co2 and 18o could have been high 18o metasedimentary country rocks the inferred change in isotopic composition of the granites is consistent with depletion of the metacarbonate rocks in 18o close to the plutons and with large volumes of fluid that were inferred from petrologic data to have infiltrated the metacarbonate rocks during metamorphism a close approach of minerals to oxygen isotope exchange equilibrium in altered mesozonal rocks from maine is in marked contrast to hydrothermally altered epizonal granites whose mineral commonly show large departures from oxygen isotope exchange equilibrium the difference in oxygen isotope systematics between altered epizonal granites and altered mesozonal granites closely parallels a differences between their mineralogical systematics both differences demonstrate the important control that depth exerts on the products of hydrothermal alteration deeper hydrothermal events occur at higher temperature and are longer lived minerals and fluid have sufficient time to closely approach both isotope exchange and heterogeneous chemical equilibrium shallower hydrothermal events occur at lower temperatures and are shorter lived generally there is insufficient time for fluid to closely approach equilibrium with all minerals