4 d imaging of subsurface changes with coda waves numerical studies of 3 d combined sensitivity kernels and applications to the m_ mathrm w m w 7 9 2008 wenchuan earthquake in the context of seismic monitoring recent studies made successful use of seismic coda waves to image the lateral extent of medium changes locating the depth of the changes however remains a challenge we use multiply scattered body and surface wave 3 d combined sensitivity kernels to address this problem we show that we can locate velocity perturbations at depth with numerical data from elastic wave field simulations in 3 d heterogeneous media this procedure is then applied to assess the extent of the crustal damage due to the m mathrm w 7 9 2008 wenchuan earthquake we discuss the potential and limitations of our approach to retrieve the depth information of temporal changes occurring in heterogeneous structures

noise based monitoring and imaging of aseismic transient deformation induced by the 2006 basel reservoir stimulation abstractwe have analyzed the time dependent properties of the ambient seismic wavefield between 0 1 and 8 hz to detect resolve monitor and image the deformation induced by the water injection associated with the stimulation of the 2006 deep heat mining project in the city of basel switzerland the application of passive methods allowed the detection of an aseismic transient of approximately 35 days duration that began with the onset of the reservoir stimulation peak deformation was reached some 15 days after the bleed off and after the induced seismicity ceased we resolved a significant increase in seismic velocities and a simultaneous decorrelation of the noise correlation coda waveforms the wavefield properties implied that the material response was monitored mainly in the sedimentary layer 2 5 km above the stimulated volume that was approximately 4 5 km deep we inverted the velocity change and decorrelation data to estimate the spatial distribution of the medium changes the resulting imag

the os and nd isotopic systematics of c 2 44 ga akanvaara and koitelainen mafic layered intrusions in northern finland abstract we have determined os and nd isotopic compositions of various rock types in and adjacent to the c 2 44 ga akanvaara and koitelainen layered intrusions which are part of the extensive paleoproterozoic ultramafic to felsic mantle plume related magmatism in the fennoscandian shield the initial e nd in the layered sequences of both intrusions fall within a limited range around 2 0 being compatible with results from other coeval layered intrusion in the shield the initial os isotopic ratios in chromitites are near chondritic the total range of os t is from 1 to 6 with the highest values reported for low os chromites no systematic differences are found in the osmium isotopic compositions of the chromites between the intrusions or relative to the stratigraphic position of the sample the studied intrusions share similar isotopic and geochemical features with rocks from younger flood basalt provinces and also the same problem of the origin of the lithospheric source component viz crustal assimilation versus melt generation within lithospheric mantle the observed nd os isotopic systematics of the intrusions require that the magmas had negative e nd values already before emplacement and can best be accounted for by 15 25 deep crustal contamination of a komatiitic melt initially having a near chondritic os isotopic composition coupled with additional minor in situ assimilation of country rock material this hypothesis is supported by the existence of coeval crustally contaminated komatiitic volcanism on the fennoscandian shield

metal silicate equilibrium in a homogeneously accreting earth new results for re the accretion and early differentiation of the earth is the starting point of earth history the abundances of metal seeking siderophile elements in the mantle are a powerful probe of those events it has long been known that siderophile element abundances in the earth s mantle are too high to have resulted from metal silicate equilibrium at near surface conditions this mismatch provided support for the idea that the earth accreted heterogeneously we report new experimental results for the highly siderophile element re and show that metal silicate partition coefficients decrease with increasing temperature at fixed pressure and relative oxygen fugacity calculations using these and previously published experimental results indicate that the abundances of the moderately siderophile elements fe ni co mo w p and most importantly the highly siderophile element re in earth s upper mantle are consistent with early equilibration between metal and silicate liquid at the base of a deep 800 1000 km magma ocean reconciliation of mantle abundances of moderately and highly siderophile elements with high temperature and pressure metal silicate equilibrium would obviate the need for heterogeneous accretion these new results indicate that the earth accreted homogeneously rather than heterogeneously or that evidence for heterogeneous accretion was erased by early high temperature and pressure melting events

potential of ambient seismic noise techniques to monitor the st gallen geothermal site switzerland the failures of two recent deep geothermal energy projects in switzerland basel 2006 st gallen 2013 have again highlighted that one of the key challenges for the successful development and operation of deep underground heat exchangers is to control the risk of inducing potentially hazardous seismic events in st gallen after an injection test and two acid injections that were accompanied by a small number of micro earthquakes ml 0 2 operators were surprised by an uncontrolled gas release from the formation gas kick the killing procedures that had to be initiated following standard drilling procedures led to a ml3 5 earthquake with ambient seismic noise cross correlations from nine stations we observe a significant loss of waveform coherence that we can horizontally and vertically constrain to the injection location of the fluid the loss of waveform coherence starts with the onset of the fluid injections 4 days prior to the gas kick we interpret the loss of coherence as a local perturbation of the medium we show how ambient seismic noise analysis can be used to assess the aseismic response of the subsurface to geomechanical well operations and how this method could have helped to recognize the unexpected reservoir dynamics at an earlier stage than the microseismic response alone allowed

monitoring velocity variations in the crust using earthquake doublets an application to the calaveras fault california we present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates we compute differences in arrival times between seismograms recorded at the same station in the freqency domain by cross correlation of short windows of signal a moving window analysis of the entire seismograms including the coda gives t the difference in arrival times versus running time along the seismogram the time resolution of the method is an order of magnitude better than the digitization interval the t technique is illustrated with a pair of microearthquakes m 1 7 and 2 0 that occurred before and after the coyote lake california earthquake m 5 9 of august 6 1979 and on the same segment of the calaveras fault that ruptured during the earthquake the coda wave arrivals for some stations are progressively delayed for the second earthquake in the doublet so that its seismogram appears as a stretched version of the earlier event we interpret this systematic variation in t along the coda as a change in the average s velocity in the upper crust in the time interval between the two doublets s wave velocities appear to have decreased by 0 2 in an oblong region 5 10 km in radius at the south end of the aftershock zone

origin and evolution of formation water at the jujo tecominoacan oil reservoir gulf of mexico part 1 chemical evolution and water rock interaction abstract the origin and evolution of formation water from upper jurassic to upper cretaceous mudstone packstone dolomite host rocks at the jujo tecominoacan oil reservoir located onshore in se mexico at a depth from 5200 to 6200 m b s l have been investigated using detailed water geochemistry from 12 producer wells and six closed wells and related host rock mineralogy saline waters of cl na type with total dissolved solids from 10 to 23 g l are chemically distinct from hypersaline cl ca na and cl na ca type waters with tds between 181 and 385 g l bromine cl and br na ratios suggest the subaerial evaporation of seawater beyond halite precipitation to explain the extreme hypersaline components while less saline samples were formed by mixing of high salinity end members with surface derived low salinity water components the dissolution of evaporites from adjacent salt domes has little impact on present formation water composition geochemical simulations with harvie m ller weare and phrqpitz thermodynamic data sets suggest secondary fluid enrichment in ca hco3 and sr by water rock interaction the volumetric mass balance between ca enrichment and mg depletion confirms dolomitization as the major alteration process potassium cl ratios below evaporation trajectory are attributed to minor precipitation of k feldspar and illitization without evidence for albitization at the jujo tecominoacan reservoir the abundance of secondary dolomite illite and pyrite in drilling cores from reservoir host rock reconfirms the observed water rock exchange processes sulfate concentrations are controlled by anhydrite solubility as indicated by positive si values although anhydrite deposition is limited throughout the lithological reservoir column the chemical variety of produced water at the jujo tecominoacan oil field is related to a sequence of primary and secondary processes including infiltration of evaporated seawater and original meteoric fluids the subsequent mixing of different water types and the formation of secondary minerals by water rock interaction a best fit between measured and calculated reservoir temperatures was obtained with the mg li geothermometer for high salinity formation water tds 180 g l whereas na k na ka ca and quartz geothermometers are partially applicable for less salinite water tds

origin of oil in the sureste basin mexico geochemical and biological marker analyses of oils and rock samples from the sureste basin of mexico were effective in identifying and geographically limiting four major oil families related by age and source rock depositional environment oxfordian tithonian early cretaceous and tertiary the source rocks giving rise to the jurassic and cretaceous oils are associated with marine carbonate environments in contrast the source rocks giving rise to the tertiary oils are associated with a marine deltaic siliciclastic depositional setting biomarker and isotope differences observed in the oils derived from marine carbonate environments can be interpreted in terms of salinity clay content and oxygen depletion variations these differences provide diagnostic criteria for recognizing and differentiating five distinct organic rich depositional regimes as the sources for these oil types an anoxic hypersaline marine carbonate environment associated with a narrow and shallow semirestricted sea oxfordian age family 1 oil an anoxic marine carbonate environment associated with a silled basin geometry tithonian age family 2 oils subtype 2a an anoxic marine carbonate environment associated with a shallow gentle broad marine carbonate ramp in a distal position tithonian age family 2 oils subtype 2b a clay rich suboxic anoxic marine carbonate environment associated with a carbonate platform in a proximal position tithonian age family 2 oils subtype 2c and an anoxic marine evaporitic environment early cretaceous age family 3 oils the tertiary oils family 4 are derived from bacterially reworked terrigenous and marine organic source materials deposited in a marine deltaic environment the tithonian related oils in the mexican southern side of the gulf of mexico accumulated both offshore and onshore and throughout the stratigraphic column from kimmeridgian to pleistocene reservoirs suggesting vertical pathways as the principal secondary migration mechanism the lateral variations of these oils can be interpreted to reflect the tithonian paleogeography in the area and could be useful in predicting differences in the oil compositions

stability of coda wave attenuation during the loma prieta california earthquake sequence the loma prieta california earthquake occurred in a densely instrumented region with a history of microearthquake recording beginning more than a decade before the october 1989 mainshock this affords an unprecedented opportunity to detect changes in seismic wave propagation in the earth s crust associated with a major earthquake in this study we use pairs of nearly identical earthquakes doublets to search for temporal changes of coda attenuation in the vicinity of the loma prieta earthquake we analyze 21 earthquake doublets recorded from 1978 to 1991 that span the preseismic coseismic and postseismic intervals and measure the change in coda q using a running window ratio of the doublet spectral amplitudes in three frequency bands from 2 to 15 hz this method provides an estimate of changes in coda q that is insensitive to other factors that influence coda amplitudes our observations place an upper bound of about 5 on preseismic coseismic and postseismic changes of coda q in the epicentral region of the loma prieta earthquake even at this low level the changes are neither spatially coherent nor correlated between adjacent frequency bands the only hint of a signal is in the preseismic data where there is a possible precursory increase in coda q of approximately 5 in the two years before the mainshock the stability of coda q throughout the loma prieta sequence is in sharp contrast to other studies that have reported much larger precursory changes in coda q for other earthquakes

plate boundary deformation and man made subsidence around geothermal fields on the reykjanes peninsula iceland abstract we present interferometric synthetic aperture radar insar data from 1992 1999 and 2003 2008 as well as gps data from 2000 2009 for the active plate boundary on the reykjanes peninsula southwest iceland the geodetic data reveal deformation mainly due to plate spreading anthropogenic subsidence caused by geothermal fluid extraction and possibly increasing pressure in a geothermal system subsidence of around 10 cm is observed during the first 2 years of production at the reykjanes geothermal power plant which started operating in may 2006 we model the surface subsidence around the new power plant using point and ellipsoidal pressure sources in an elastic halfspace short lived swarms of micro earthquakes as well as aseismic fault movement are observed near the geothermal field following the start of production possibly triggered by the stresses induced by geothermal fluid extraction

the petrogenesis of gorgona komatiites picrites and basalts new field petrographic and geochemical constraints gorgona island colombia is remarkable not only because it contains the only phanerozoic komatiites but also because it has mafic to ultramafic lavas with a wide range of compositions from moderately enriched to extremely depleted relative to bulk earth the komatiite flows are in many respects similar to archaean komatiites they formed from mgo rich 18 liquids and have upper spinifex zones and lower cumulate zones the cumulate zones of archaean komatiites contain many solid grains in contrast more than 90 of the olivine in the gorgona cumulates is highly skeletal this combined with the fact that the gorgona cumulate zones are thinner than those in archaean komatiites suggests that the komatiite magma became strongly superheated en route to the surface the komatiites have trace element contents intermediate between those of the basalts and the ultramafic tuffs some basalts have isotope compositions indicative of long term enrichment in incompatible elements whereas other basalts and ultramafic volcanics have isotopic signatures that imply corresponding depletion it is apparent that the plume source region of the gorgona magmas was markedly heterogeneous with at least two source components contributing to the observed variation in composition this heterogeneity may have resulted from the incorporation of different components into the plume source or it may be the result of complex melting and melt extraction processes during the ascent of a heterogeneous plume despite earlier suggestions that there may have been a significant age gap between depleted komatiite and basalt flows and the enriched basal new 4oar 39ar dating of basalts and gabbros are more consistent with all being generated at 87 ma during formation of the caribbean colombian plateau possibly at the galapagos hotspot

ocean ridge discontinuities in iceland abstract the tjornes fracture zone in north iceland and the south iceland seismic zone are ocean ridge discontinuities that are partly exposed on land these are zones of high seismicity but contrasting style of crustal deformation detailed field studies and numerical modelling suggest that the tjornes fracture zone has all the characteristics of an oceanic transform fault is 7 9 ma old and developed along the zone of maximum shear stress between the nearby tips of the rift zones of the kolbeinsey ridge and north iceland conversely the results indicate that the south iceland seismic zone developed within an area of shear stress concentration between the overlapping rift zones in south iceland the development of the south iceland seismic zone is a consequence of the propagation of the eastern rift zone to the southwest during the past 3 ma

ambient noise tomography of the greater geneva basin in a geothermal exploration context the greater geneva basin is one of the key targets for geothermal exploration in switzerland until recently information about the subsurface structure of this region was mostly composed of well logs seismic reflection lines and gravity measurements as part of the current effort to further reduce subsurface uncertainty and to test passive seismic methods for exploration purposes we performed an ambient noise tomography of the greater geneva basin we used 1 5 years of continuous data collected on a temporary seismic network composed of 28 broadband stations deployed within and around the basin from the vertical component of the continuous noise recordings we computed cross correlation functions and retrieved rayleigh wave group velocity dispersion curves we then inverted the dispersion curves to obtain 2d group velocity maps and proceeded to a subsequent inversion step to retrieve a large scale 3d shear wave velocity model of the basin we discuss the retrieved features of the basin in the light of local geology previously acquired geophysical datasets and ongoing geothermal exploration the greater geneva basin is an ideal natural laboratory to test innovative geothermal exploration methods because of the substantial geophysical datasets available for comparison while we point out the limits of ambient noise exploration with sparse networks and current methodology we also discuss possible ways to develop ambient noise tomography as an affordable and efficient subsurface exploration method

osmium isotopes in ophiolites re and os concentrations and os isotopic composition are reported for ultramafic samples from ophiolites these data may be divided into two groups on the one hand isotopic values higher than mean upper mantle 187os 186os 1 05 correspond to back arc type ophiolites and could reflect injection of crustal material sediments on the other hand ophiolites referred to as being typical n morb plot very close to previous estimates for mean upper mantle 1 05 together with refined osmiridium results from well dated ultramafic suites the data on ophiolites lead to the following constraints 1 present day 187os 186os for the upper mantle seems for the time being constrained around 1 05 1 06 2 the mantle evolution curve for osmium isotopes through time when associated to recent os isotopic determinations from the literature for archaean samples shows a chondritic 187re 186os ratio of 3 33 and a linear closed system evolution

physical and chemical controls on the composition of waters in sedimentary basins abstract the composition of subsurface waters is determined not only by diagenetic reactions but also by physical processes of fluid convection and hydrodynamic dispersion the south west louisiana gulf coast provides an instructive field example of the net effects of diagenetic reaction and solute transport on pore water compositions in a regional siliciclastic sequence most formation waters here have compositions totally unlike the compositions of the connate meteoric and marine fluids that were buried with their host sediments at the time of deposition dissolved chloride has been generated by the subsurface dissolution of salt domes and has been pervasively transported by fluid flow throughout most of the upper 3 km of the sedimentary section the simultaneous systematic variation in dissolved na k mg ca and alkalinity with chloride in these waters supports the hypothesis that metastable thermodynamic buffering by silicate carbonate mineral assemblages is a first order control on fluid compositions the chemical potential of chloride or alternatively total anionic charge appears to be a master variable which ranks in importance with such other variables as pressure and temperature in driving diagenesis in this region this variable is controlled largely by physical processes of advection and dispersion in the upper 3 km of the section and by dehydration reactions in deeper mudstone dominated sediments where the composition of the fluid is largely rock buffered the ultimate origin of the fluid and its pathway of chemical evolution may be obscured at least in terms of major solute composition non buffered components such as cl and br or isotopic compositions are more likely to retain information on original end member fluid compositions and reaction pathways

short and long term variations in the reykjanes geothermal reservoir from seismic noise interferometry the reykjanes geothermal system rgs is a high temperature geothermal system located on the reykjanes peninsula a transtensional plate boundary zone located on the southwestern tip of iceland the area is characterized by high seismicity recent volcanism and high temperature geothermal fields we use seismic noise records from april 2014 to august 2015 to study stress changes and potential deformation of the subsurface caused by injection and production operations at rgs through seismic interferometry we retrieve continuous time series of waveform similarity values and seismic velocity changes during this period the s transform of the similarity values allows us to clearly identify three variations in the mechanical properties of the reykjanes peninsula related to rapid changes of rgs production in addition we observe a slow seismic velocity decrease of 0 36 year in the reservoir due to the water deficit and seasonal variations associated with the energy production demand

mapping the basement of the ebro basin in spain with seismic ambient noise autocorrelations this work is funded by the spanish project misterios cgl2013 48601 c2 1 r we also acknowledge support and discussion through tides cost action es1401

monitoring stress changes in a concrete bridge with coda wave interferometry coda wave interferometry is a recent analysis method now widely used in seismology it uses the increased sensitivity of multiply scattered elastic waves with long travel times for monitoring weak changes in a medium while its application for structural monitoring has been shown to work under laboratory conditions the usability on a real structure with known material changes had yet to be proven this article presents experiments on a concrete bridge during construction the results show that small velocity perturbations induced by a changing stress state in the structure can be determined even under adverse conditions theoretical estimations based on the stress calculations by the structural engineers are in good agreement with the measured velocity variations

estimating the wet rock p wave velocity from the dry rock p wave velocity for pyroclastic rocks seismic methods are widely used for the geotechnical investigations in volcanic areas or for the determination of the engineering properties of pyroclastic rocks in laboratory therefore developing a relation between the wet and dry rock p wave velocities will be helpful for engineers when evaluating the formation characteristics of pyroclastic rocks to investigate the predictability of the wet rock p wave velocity from the dry rock p wave velocity for pyroclastic rocks p wave velocity measurements were conducted on 27 different pyroclastic rocks in addition dry rock s wave velocity measurements were conducted the test results were modeled using gassmann s and wood s theories and it was seen that estimates for saturated p wave velocity from the theories fit well measured data for samples having values of less and greater than 20 practical equations were derived for reliably estimating wet rock p wave velocity as function of dry rock p wave velocity

lapse time dependent coda wave depth sensitivity to local velocity perturbations in 3 d heterogeneous elastic media in the context of seismic monitoring recent studies made successful use of seismic coda waves to locate medium changes on the horizontal plane locating the depth of the changes however remains a challenge in this paper we use 3 d wavefield simulations to address two problems first we evaluate the contribution of surface and body wave sensitivity to a change at depth we introduce a thin layer with a perturbed velocity at different depths and measure the apparent relative velocity changes due to this layer at different times in the coda and for different degrees of heterogeneity of the model we show that the depth sensitivity can be modelled as a linear combination of body and surface wave sensitivity the lapse time dependent sensitivity ratio of body waves and surface waves can be used to build 3 d sensitivity kernels for imaging purposes second we compare the lapse time behaviour in the presence of a perturbation in horizontal and vertical slabs to address for instance the origin of the velocity changes detected after large earthquakes

lip reading recognizing oceanic plateaux in the geological record basaltic oceanic plateaux are important features in the geological record not only do they record ancient mantle plume activity but they also are believed to be important building blocks in the formation of the continental crust in this paper we review the salient features of two cretaceous oceanic plateaux the ontong java and the caribbean colombian thick sequences of predominantly homogeneous basalt the occurrence of high mgo basalt including komatiites and an apparent absence of sheeted dyke complexes in addition pyroclastic deposits may be scarce we then explore ways of distinguishing plateaux from basaltic sequences erupted in different tectonomagmatic settings continental flood basalt provinces island arcs back arc basins ocean islands and mid ocean ridges using these criteria potential archaean and proterozoic oceanic plateaux are reviewed and identified finally we explore how these remnant oceanic plateaux became incorporated into the continents by reviewing the proposed accretion mechanisms for the cretaceous caribbean colombian oceanic plateau on the basis of evidence from south america and the tonalites of the southern caribbean island of aruba

detecting and locating precursory signals during the 2011 el hierro canary islands submarine eruption pilar sanchez pastor acknowledges funding from the spanish ministry of economy and competitiveness project misterios cgl2013 48601 c2 2 r

coda wave interferometry for estimating nonlinear behavior in seismic velocity in coda wave interferometry one records multiply scattered waves at a limited number of receivers to infer changes in the medium over time with this technique we have determined the nonlinear dependence of the seismic velocity in granite on temperature and the associated acoustic emissions this technique can be used in warning mode to detect the presence of temporal changes in the medium or in diagnostic mode where the temporal change in the medium is quantified

imaging preeruptive and coeruptive structural and mechanical changes of a volcano with ambient seismic noise 1 forecasting the location of an eruption is of primary importance for risk management in volcanic regions locating the underground structural changes associated with a potential eruption is also a key issue to better understand the dynamics at work in a volcano using recent results in wave physics we develop an imaging procedure that is based on the sensitivity of multiply scattered waves to weak changes in heterogeneous media this procedure allows to locate changes in both mechanical and scattering properties of the studied medium we study ambient seismic noise from 19 broadband stations at the active volcano piton de la fournaise on reunion island recorded from june to december 2010 during this period two volcanic eruptions occurred at two different locations we calculate the noise cross correlations and study two types of changes in the coda apparent velocity variations related to changes in the elastic properties of the medium and waveform decoherence associated with variations in the scattering and thus the geological structures we observe that the temporal variations of both of these parameters provide potential precursors of volcanic eruptions at piton de la fournaise the locations determined from the preeruptive and coeruptive changes in both parameters are in good agreement with the actual eruptive activities these data demonstrate that the coda of ambient noise correlations contains deterministic information on the locations of the eruptive processes in an active volcano our analysis offers an original and significant constraint for the localization of forthcoming volcanic eruptions

the occurrence and origin of methane in some groundwater flow systems the origin of methane in selected groundwater flow systems is investigated through carbon isotope geochemical studies combined with hydrogeological and hydrogeochemical information methane is a common trace constituent in these groundwaters and occasionally constitutes a major carbon pool two modes of origin for methane are commonly recognized microbial production biogenic methane and non biological chemical production thermocatalytic methane in the groundwaters sampled the few thermocatalytic methanes encountered have 13c values greater than about 45 whereas the more common normal biogenic methanes have 13c values less than about 60 biogenic methanes from sanitary landfill sites have intermediate 13c values of about 38 to 56 and so can easily be distinguished from normal biogenic methane the carbon source for biogenic methane is usually organic matter present in the aquifer materials the carbon isotope ratios of dissolved methane and total inorganic carbon in sampled groundwaters ar

platinum group element distribution in komatiitic and tholeiitic volcanic rocks from munro township ontario platinum pd ir au mgo cr s ni co cu and zn were determined in volcanic rocks from pyke hill fred s flow and theo s flow in munro township ontario to establish the fractionation trends of the platinum group elements in these rocks and to evaluate the relevant processes controlling such fractionation distinctive and relatively consistent fractionation trends are characteristic of pt pd and ir platinum and pd are usually concentrated in the upper units of flows spinifex textured rocks relative to the lower olivine and pyroxene rich cumulates whereas the reverse is true for ir theo s flow does not show these patterns in that pt pd and ir behave in a similar fashion the platinum group element fractionation trends formed during the crystallization of these flows suggest that sulfide immiscibility has an insignificant role it is concluded that in general ir must be coprecipitated with olivine or pyroxene whereas pt and pd are rejected from the structures of these minerals the ir ferromagnesian association probably does not involve a substitution of ir in the mineral structure of olivine or pyroxene

recent cross formational fluid flow and mixing in the shallow michigan basin ground water with total dissolved solids tds ranging from 10 to 50 g l exists at depths between 90 and 140 m in devonian oil bearing formations in the shallow michigan basin of southwestern ontario these formations comprise mainly limestone and dolomite and the sources of the saline ground water have not been identified previously isotopic and major ion data from ground water from devonian oil bearing formations in southwestern ontario indicate that the highest salinity fluids were emplaced locally from depths of several hundred meters during the later stages of or following the wisconsinan glaciation saline water and petroleum were also emplaced into overlying pleistocene clay rich glacial deposits isostatic rebound leading to fracturing and enhanced formation permeability due to matrix expansion was probably the primary mechanism that enabled these saline fluids to migrate into discrete areas of the devonian and pleistocene formations the geochemical data presented here support a model involving cross formational fluid flow from depth occurring vertically on the scale of several hundred meters since glaciation the hydrogeologic regime in this shallow basinal system must therefore be viewed as dynamic rather than static to depths of at least 500 m over a time frame of 100 000 yr 54 refs 10more figs 2 tabs less

seismic noise correlations to image structural and mechanical changes associated with the mw 7 9 2008 wenchuan earthquake we locate temporal changes of seismic wave speed and scattering properties of the crust associated with the 2008 mw7 9 wenchuan earthquake to that end we analyze ambient seismic noise records from 2007 until the end of 2008 in the 1 3 s period band and in the 12 20 s period band measured in a region that covers the southern two thirds of the fault activated during the earthquake to locate the changes we use a refined imaging procedure based on the sensitivity of scattered waves to weak perturbations this inverse method uses the radiative transfer approximation to describe the intensity of the noise correlation coda our results show that the largest structural changes are observed northeast of the wenchuan epicenter around the fault zone where aftershocks are distributed the spatial and temporal characteristics of the behavior of the crust at depth around the wenchuan earthquake suggest a postseismic and geology dependent signature of the middle crust we also observe a clear seasonal signature within the sichuan basin at depth that we relate to the heavy rainfalls during the monsoon season this seasonality can also be observed at the surface in form of a waveform decoherence our study highlights that seismic velocity changes and waveform decoherence are independent measurements that are sensitive to different parameters and can thus give complementary information in our study we also point out the value of studying the evolution of the changes at different times in the coda

isotopic geochemistry of burial metamorphosed volcanogenic sediments great valley sequence northern california isotopic and mineralogic data from an 8500 m thick section of the great valley sequence northern california indicate that changes in the 18o values of authigenic minerals resulted from the conversion of smectite to a 10 a clay mineral as temperature increased with burial in the jurassic cretaceous outer arc basin the clay mineral assemblage in mudstone is characterized by a proportional increase of the 10 a clay mineral with increasing stratigraphic depth and by a depletion in the 18o value of the mixed layer smectite 10 a clay mineral with descending stratigraphic position from 21 9 to 15 5 smow modeling of the oxygen isotopic data from authigenic phases based on equilibrium fractionation during clay mineral diagenesis indicates that 18o values of calcite in mudstones and of calcite cements in sandstone precipitated along a temperature gradient of about 25 c km during maximum burial to about 6 7 km d values of the mixed layer smectite 10 a clay mineral range between 69 to 44 smow using temperatures calculated from the oxygen isotopic data the deuterium and oxygen isotopic data indicate that the smectite underwent late stage dehydration and probably buffered the composition of formation waters from sea water values to isotopic compositions of 18o 8 smow and d 25 smow the 13c values of calcite from mudstone and sandstone imply that crystallization of authigenic calcite was linked to organic diagenesis during which dissolved hcot 3 was continuously enriched in 13c as temperature increased with burial at the base of the sequence and immediately overlying the ophiolitic basement rocks several hundred meters of strata were altered by more oxygen depleted 18o 4 to 5 hydrothermal fluids emanating from the ophiolitic rocks probably at maximum burial depth

infrasonic ambient noise interferometry from correlations of microbaroms 1 we show that microbaroms continuous infrasound fluctuations resulting from the interaction of the ocean with the atmosphere have long range correlation properties that make it possible to estimate the impulse response between two microphones from passive recordings the processing is analogous to methods employed in the emerging field of ambient noise seismology where the random noise source is the ocean coupling with the solid earth microseisms instead of the atmosphere microbaroms we find that time dependent temperature fields and temperature inversions determine the character of infrasonic impulse responses at fourpeaked volcano in alaska applications include imaging and monitoring the gross structure of the earth s atmospheric boundary layer

pyroclastic rocks another manifestation of ultramafic volcanism on gorgona island colombia tertiary ultramafic volcanism on gorgona island colombia is manifested not only by komatiite flows but also by a more voluminous sequence of tuff breccias which is cut by comagmatic picrite dikes the ultramafic pyroclastic rocks are chaotic to stratified mixtures of angular to subrounded glassy picritic blocks and a fine grained volcaniclastic matrix that consists primarily of plastically deformed glassy globules the entire deposit is interpreted to have formed by an explosive submarine eruption of phenocryst laden picritic magma mgo contents of tuff breccias and picrite dikes range from 21 to 27 wt relative to nearby komatiite flows these rocks are mgo rich and feo tio2 and ni poor hree concentrations are very low seven times chondrite and similar to those of the komatiites whereas the lree are extremely fractionated ce sm n 0 2 indicating derivation from a more highly depleted mantle source region nd isotopic data suggest a cogenetic relationship between the picritic magma that formed the tuff breccia and associated dikes and that which produced the komatiite flows nevertheless pb isotopic data as well as whole rock geochemistry preclude such a connection either due to olivine fractionation accumulation or to different degrees of partial melting these ultramafic rock types crystallized from magmas which most likely were extracted from distinct mantle source regions

os pb and nd isotope geochemistry of the permian emeishan continental flood basalts insights into the source of a large igneous province abstract the nature of the source of continental flood basalts cfb is a highly debated topic proposed mantle sources for cfbs including both high and low ti basalts include subcontinental lithospheric mantle sclm asthenospheric mantle and deep plume related mantle re os isotope systematics can offer important constraints on the sources of both ocean island basalts oib and cfb and may be applied to distinguish different possible melt sources this paper reports the first re os isotope data for the late permian emeishan large igneous province lip in southwest china twenty one cfb samples including both low and high ti basalts from five representative sites within the emeishan lip have been analyzed for os nd and pb isotopic compositions the obtained os data demonstrate that crustal assimilation affected os isotopic compositions of some emeishan basalt samples with low os concentrations but not all of the samples and the emeishan basalts with high os contents likely experienced the least crustal contamination the low and high ti basalts yield distinct os signatures in terms of 187os 188os and os content the low ti basalt with the highest os concentration 400 ppt has a radiogenic os isotopic composition os t 6 5 similar to that of plume derived oib because the os isotopic composition of basalts with relatively high os concentrations typically 50 ppt likely represents that of their mantle source this result implies a plume derived origin for the low ti basalts on the other hand the high ti basalts with high os concentration over 50 ppt have unradiogenic os isotopic signatures os t values range from 0 8 to 1 4 suggesting that a subcontinental lithosphere mantle sclm component most likely contributed to the generation of these magmas combining pb and nd isotopic tracers with the os data we demonstrate that the low ti basaltic magmas in the emeishan cfb were mainly sourced from a mantle plume reservoir whereas the high ti basaltic magmas were most likely derived from a sclm reservoir or were contaminated by a significant amount of lithospheric mantle material during plume related magma ascent through the sclm

comparative reos smnd and rbsr isotope and trace element systematics for archean komatiite flows from munro township abitibi belt ontario abstract a series of komatiite flows from munro township ontario have re and os concentrations that range from 0 545 to 1 27 ppb and 1 00 to 2 20 ppb respectively the187re 186os in the suite range from 14 05 to 52 37 and the187os 186os range from 1 49 to 3 22 giving a crystallization age of2726 93ma and an of initial187os 186os of0 873 0 035 this age is in good agreement with the crystallization ages that have been reported for these rocks using other isotopic systems the re os isochron indicates that the system was resistant to the low grade metamorphism that altered the rocks the initial os isotopic composition is consistent with the derivation of the melts from a mantle source s that originated with a chrondritic 187os 186os i and evolved with an approximately chondriticre os sm nd data for the same suite cluster about anend value at 2 72 ga of 2 to 3 rb sr isotope data indicate significant mobilization of these elements by the greenschist grade metamorphism that has altered the rocks comparisons of re and os concentrations with those of mgo feo ni cr and s suggests that re was incompatible d 1 os concentrations were likely controlled by the presence or precipitation of trace metallic or sulfide phases both during melting and crystallization and not by the modally predominant silicate minerals

pb isotopes of gorgona island colombia isotopic variations correlated with magma type abstract lead isotopic results obtained on komatiites and basalts from gorgona island provide evidence of large isotopic variations within a restricted area 8 2 5 km the variations are correlated with differences in volcanic rock type the highest isotopic ratios 206 pb 204 pb 19 75 correspond to tholeiites which make up most of the island the lowest ratios 18 3 correspond to the komatiites of the west coast of the island other rock types komatiites of the east coast k tholeiites picrites and tuffs have isotopic characteristics intermediate between these two extreme values these results are explained by the existence of two distinct mantle source regions and by mixing or contamination between them

improving temporal resolution in ambient noise monitoring of seismic wave speed 1 the use of ambient seismic noise has been intensively investigated to perform passive tomography at various scales besides passive tomography passive monitoring is another application of seismic noise correlation as was shown by the recent observation of postseismic velocity changes around the san andreas fault in parkfield california one of the drawbacks of using ambient noise correlation for passive monitoring is the need to average the correlations over a long time period in order to obtain a sufficient signal to noise ratio snr for the phase fluctuations to be measured accurately for the application to passive monitoring one wants the possibility of following short term velocity variations 1 day or less using noise correlation functions calculated on short time windows another difficulty may then appear when the spatial distribution of noise sources also evolves with time the aim of this paper is to introduce an adaptive filter to the parkfield data set in order to improve the snr output of the ambient noise correlation functions when applied to passive monitoring the temporal resolution can be increased from 30 days up to 1 day with this improved temporal resolution the velocity drop observed at parkfield is shown to be cosesimic with the 24 september 2004 mw 6 0 event the relationship between the measured velocity fluctuations and the time evolution of the spatial distribution of the noise wavefield is also investigated finally the error bar in the amplitudes of the velocity variations is compared with a theoretical expectation

mapping pressurized volcanic fluids from induced crustal seismic velocity drops volcanic eruptions are caused by the release of pressure that has accumulated due to hot volcanic fluids at depth here we show that the extent of the regions affected by pressurized fluids can be imaged through the measurement of their response to transient stress perturbations we used records of seismic noise from the japanese hi net seismic network to measure the crustal seismic velocity changes below volcanic regions caused by the 2011 moment magnitude m w 9 0 tohoku oki earthquake we interpret coseismic crustal seismic velocity reductions as related to the mechanical weakening of the pressurized crust by the dynamic stress associated with the seismic waves we suggest therefore that mapping seismic velocity susceptibility to dynamic stress perturbations can be used for the imaging and characterization of volcanic systems

assessment of resolution and accuracy of the moving window cross spectral technique for monitoring crustal temporal variations using ambient seismic noise summary temporal variations in the elastic behaviour of the earth s crust can be monitored through the analysis of the earth s seismic response and its evolution with time this kind of analysis is particularly interesting when combined with the reconstruction of seismic green s functions from the cross correlation of ambient seismic noise which circumvents the limitations imposed by a dependence on the occurrence of seismic events in fact because seismic noise is recorded continuously and does not depend on earthquake sources these cross correlation functions can be considered analogously to records from continuously repeating doublet sources placed at each station and can be used to extract observations of variations in seismic velocities these variations however are typically very small of the order of 0 1 per cent such accuracy can be only achieved through the analysis of the full reconstructed waveforms including later scattered arrivals we focus on the method known as moving window cross spectral analysis that has the advantage of operating in the frequency domain where the bandwidth of coherent signal in the correlation function can be clearly defined we investigate the sensitivity of this method by applying it to microseismic noise cross correlations which have been perturbed by small synthetic velocity variations and which have been randomly contaminated we propose threshold signal to noise ratios above which these perturbations can be reliably observed such values are a proxy for cross correlation convergence and so can be used as a guideline when determining the length of microseismic noise records that are required before they can be used for monitoring with the moving window cross spectral technique

hydrochemical isotopic tendencies to define hydraulic mobility of formation water at the samaria sitio grande oil field mexico abstract the chemical major elements and isotopic 2 h 3 h 13 c 18 o composition of formation water is presented for the sitio grande oilfield se mexico extracted from 28 production wells from the carbonate reservoir at a depth between 3585 and 4545 m b s l the linear 18 o d trend explains the formation of reservoir water as part of three subsequent stages a the evaporation of marine water at the surface causing enrichment of both 18 o and d values b a reversal trend with decreasing 18 o and d ratios by the extreme evaporation of brines and c the subsequent mixing with isotopically depleted meteoric water a sw ne directed flow direction of deep groundwater systems is indicated by parallel oriented isoline trends of stable isotope ratios and conservative elements supported by the dominance of parallel directed microfractures and extensional faults and by tracer test results the arrival of artificial tritium three years after tracer injection in the well sg 85 reflects a the importance of long term monitoring of tracer tests and b an estimated flow velocity of 2 2 10 5 m s as the arrival of the tracer was detected exclusively in three production wells towards the sw of the injection site lateral migration of groundwater occurs mainly along defined channel like conducts with a narrow dispersion angle of 39 surface water injected as part of an enhanced oil recovery program was not detected in the production zone by chemical and isotopic methods this fact is not a proof for lacking hydraulic conductivity as the large reservoir size and the termination of the injection program in 1996 could have caused a complete dilution of the injected fluids restricted vertical flow movement between reservoir layers and insignificant temperature dependent reaction processes is indicated by the heterogeneous distribution of 18 o and cl values throughout the groundwater column of most reservoir zones little influence of water rock interaction such as ca mg exchange processes between formation water and host rock is reflected by the heterogeneous abundance of calcium in the liquid phase in both dolomite free and dolomitized carbonate host rock layers

time distance helioseismology the application of seismology to the study of the solar interior1 2 helioseismology has advanced almost solely by the prediction and measurement of the sun s frequencies of free oscillation or normal modes direct measurement of the travel times and distances of individual acoustic waves the predominant approach in terrestrial seismology3 would appear to be more difficult in view of the number and stochastic nature of solar seismic sources here however we show that it is possible to extract time distance information from temporal cross correlations of the intensity fluctuations on the solar surface this approach opens the way for seismic studies of local solar phenomena such as subsurface in homogeneities near sunspots and should help to refine global models of the internal velocity stratification in the sun

origin and evolution of formation water at the jujo tecominoacan oil reservoir gulf of mexico part 2 isotopic and field production evidence for fluid connectivity abstract the chemical and isotopic characterization of formation water from 18 oil production wells extracted from 5200 to 6100 m b s l at the jujo tecominoacan carbonate reservoir in se mexico and interpretations of historical production records were undertaken to determine the origin and hydraulic behavior of deep groundwater systems the infiltration of surface water during late pleistocene to early holocene time is suggested by 14c concentrations from 2 15 to 31 86 pmc and by 87sr 86sr ratios for high salinity formation water 0 70923 0 70927 that are close to the composition of holocene to modern seawater prior to infiltration the super evaporation of seawater reached maximum tds concentrations of 385 g l with lowest 18o values characterizing the most hypersaline samples minor deviations of formation water and dolomite host rocks from modern and jurassic 87sr 86sr seawater composition respectively suggest ongoing water rock interaction and partial isotopic equilibration between both phases the abundance of 14c in all sampled formation water 87sr 86sr ratios for high salinity water close to holocene present seawater composition a water salinity distribution that is independent of historic water cut and a total water extraction volume of 2 037 mmm3 1 83 4 07 excludes a connate oil leg origin for the produced water of the jurassic cretaceous mudstone dolomite sequence temporal fluctuations of water chemistry in production intervals the accelerated migration of water fronts from the reservoir flanks and isotopic mixing trends between sampled wells confirms the existence of free aquifer water below oil horizons vertical and lateral hydraulic mobility has probably been accelerated by petroleum extraction the combination of interpreting historical fluctuations of salinity and water percentage in production wells with chemical isotopic analysis of formation water resulted in a successful method to distinguish four groundwater bodies stratified vertically within the jujo tecominoacan reservoir two with low tds from 10 to 23 g l are preserved in the upper reservoir section mainly in lower cretaceous and kimmeridgian strata for the deeper part of the reservoir 87sr 86sr trends indicate an affiliation of most samples to two independent mixing trends between intermediate saline tds 200 g l and hypersaline 350 g l groundwater end members

depth sensitivity of seismic coda waves to velocity perturbations in an elastic heterogeneous medium summary numerous monitoring applications make use of seismic coda waves to evaluate velocity changes in the earth this raises the question of the spatial sensitivity of coda wave based measurements here we investigate the depth sensitivity of coda waves to local velocity perturbations using 2 d numerical wavefield simulations we calculate the impulse response at the surface before and after a slight perturbation of the velocity within a thin layer at depth is introduced we perform a parametric analysis of the observed apparent relative velocity changes e obs versus the depth of the thin perturbed layer through the analysis of the decay of e obs we can discriminate two different regimes one for a shallow perturbation and the other for a deep perturbation we interpret the first regime as the footprint of the 1 d depth sensitivity of the fundamental surface wave mode to interpret the second regime we need to model the sensitivity of the multiply scattered body waves in the bulk we show that the depth sensitivity of coda waves can be modelled as a combination of bulk wave sensitivity and surface wave sensitivity the transition between these two regimes is governed by mode conversions due to scattering we indicate the importance of surface waves for the sensitivity of coda waves at shallow depths and at early times in the coda at later times bulk waves clearly dominate the depth sensitivity and offer the possibility of monitoring changes at depths below the sensitivity of the surface waves based on the transition between the two regimes we can discriminate a change that occurs at the surface from a change that occurs at depth this is illustrated for shallow depth perturbations through an example from lunar data

rhenium osmium isotope and platinum group elements in the xinjie layered intrusion sw china implications for source mantle composition mantle evolution pge fractionation and mineralization abstract the xinjie mafic ultramafic layered intrusion in the emeishan large igneous province elip hosts cu ni platinum group element pge sulfide ore layers within the lower part and fe ti v oxide bearing horizons within the middle part the major magmatic cu ni pge sulfide ores and spatially associated cumulate rocks are examined for their pge contents and re os isotopic systematics the samples yielded a re os isochron with an age of 262 27 ma and an initial 187 os 188 os of 0 12460 0 00011 os t 0 5 0 1 the age is in good agreement with the previously reported u pb zircon age indicating that the re os system remained closed for most samples since the intrusion emplacement they have near chondritic os t values ranging from 0 7 to 0 2 similar to those of the lijiang picrites and song da komatiites exceptionally two samples from the roof zone and one from upper sequence exhibit radiogenic os t values 0 6 to 8 6 showing minor contamination by the overlying emeishan basalts the pge rich ores contain relatively high pge and small amounts of sulfides generally less than 2 and the abundance of cu and pge correlate well with s implying that the distribution of these elements is controlled by the segregation and accumulation of a sulfide liquid some ore samples are poor in s mostly t and cr tio 2 ratios immediately below units 2 4 together with high cu zr ratios decreasing from each pge ore layer within these cyclic units are consistent with multiple magma replenishment episodes the sulfides in the cumulate rocks show little evidence of pge depletion with height and thus appear to have segregated from successive inputs of fertile magma this suggests that the xinjie intrusion crystallized from in an open magma system e g a magma conduit the compositions of the disseminated sulfides in most samples can be modeled by applying an r factor silicate sulfide mass ratio of between 1000 and 8000 indicating the segregation of only small amounts of sulfide liquid in the parental ferropicritic magmas thus continuous mixing between primitive ferropicritic magma and differentiated resident magma could lead to crystallization of chromite cr bearing magnetite and subsequently abundant fe ti oxides thereby the segregation of pge rich cu sulfide when considered in the light of previous studies on plume derived komatiites and picrites worldwide the close to chondritic os isotopic composition for most xinjie samples lijiang picrites and song da komatiites suggest that the ferropicritic magma in the elip were generated from a plume this comprised recycled neoproterozic oceanic lithosphere including depleted peridotite mantle embedded with geochemically enriched domains the ascending magmas thereafter interacted with minor possibly

mechanisms driving groundwater flow near salt domes groundwater flow near salt domes is complex because groundwater is subject to a variety of driving forces including the release of geopressured fluids large lateral density gradients and regional hydraulic head gradients the complexity of this environment is born out by recent geochemical and geophysical observations that indicate the occurrence of upward groundwater flow near some salt domes in order to evaluate the relative importance of different mechanisms driving groundwater flow near salt domes the authors have developed a numerical model that couples groundwater flow heat transport and transport of dissolved salt and accounts for salt diapirism the calculations indicate that upward groundwater flow can occur as the result of thermal convection when the regional background salinity is greater than 15 weight percent a value typical of many areas of the south louisiana salt dome province for lower background salinities dissolution causes salt laden groundwater near the dome to sink leading to depressed isotherms while the release of geopressured fluids is difficult to quantify it remains a likely mechanism for driving upward groundwater flow near some salt domes

implications of 187os isotopic heterogeneities in a mantle plume evidence from gorgona island and curacao recent work has suggested that the mafic ultramafic volcanism in evidence throughout portions of the caribbean central america and northern south america including the islands of gorgona and curacao was generated as part of a middle cretaceous large igneous province new re os isochron results for tholeiitic basalts from gorgona and curacao indicate crystallization ages of 89 2 5 2 and 85 6 8 1 ma respectively consistent with reported ar ages the gorgona ultramafic suite shows a large range in initial os isotopic composition with os values ranging from 0 5 to 12 4 this large range reflects isotopic heterogeneities in the mantle source similar to those observed for modern ocean island basalts in contrast to ocean island basalts however os isotopic compositions do not correlate with variations in nd sr or pb isotopic compositions which are within the range of depleted mid ocean ridge basalts the processes that produced these rocks evidently resulted in the decoupling of os isotopes from the nd sr and pb isotopic systems picrites from curacao have very uniform chondritic initial os isotopic compositions with initial os values ranging only from 0 4 to 1 4 basalts from curacao however define an isochron with a 187os enriched initial isotopic composition os 9 5 in contrast to the 187os enriched ultramafic rocks from gorgona the enrichment in these basalts could have resulted from lithospheric contamination if the gorgona and curacao rocks were derived from the same plume os results combined with sr nd and pb data indicate a heterogeneous plume with multiple compositionally and isotopically distinct domains the os isotopic results require derivation of os from a minimum of two distinct reservoirs one with a composition very similar to the chondritic average and one with long term enriched re os oceanic crustal recycling has been invoked to explain most of the 187os enrichments that have been observed in ocean island basalt sources and could potentially apply to the gorgona suite crustal recycling however requires large proportions of very ancient recycled basaltic crust in the sources of the 187os enriched ultramafic rocks to explain the magnitude of 187os enrichments observed for example addition of 20 oceanic crust to fertile mantle and nearly 3 billion years are necessary to generate a reservoir with the os isotopic composition of the most radiogenic komatiites if the recycled oceanic crust was added to basalt depleted mantle as may be indicated by nd values for the komatiites averaging about 10 even larger proportions of older crust are required large proportions of oceanic mafic crust in the sources of the 187os enriched komatiites although petrologically conceivable under certain melting conditions is unlikely here given the limited trace element and lithophile isotope system variations these results raise questions about the efficacy of using os isotopes to constrain the proportion of recycled oceanic crust in other plumes other possible mechanisms for generating 187os enriched mantle include invoking the existence of a 187os enriched lower mantle and minor outer core lower mantle interactions

conceptual hydrochemical model of late pleistocene aquifers at the samario sitio grande petroleum reservoir gulf of mexico mexico carbon 14 concentrations between 0 83 and 11 79 pmc of formation water from the activo samaria sitio grande petroleum reservoir in se mexico extracted from 3500 to 4500 m b s l indicate a common infiltration event of surface water during the late pleistocene period mixing of two components meteoric water and seawater previously evaporated at the surface explain the widespread mineralization tdi 15 257 g l of na cl and na ca cl type reservoir water statistical discrimination by clustering and a heterogeneous chemical isotopic fluid composition indicate the existence of 4 different water types as part of local aquifer systems which are separated by normal and thrust faults tectonic horst and graben structures show an ambiguous individual hydraulic behaviour as permeable conduits and or as impermeable barriers causing the local limitation of aquifer extent the recent increase of water production in petroleum wells is not related to the injection of surface water but the long term extraction of oil reserves is modifying the original position and flow direction of the reservoir aquifers the rise of the initial groundwater level reflects the final stage of an exhausted petroleum reservoir with coning effects of underlying aquifer systems the flexible change towards superior production intervals could represent a feasible technique to avoid the abrupt closure of invaded production wells

platinum group elements in kostomuksha komatiites and basalts implications for oceanic crust recycling and core mantle interaction we report precise pge os ir ru pt and pd concentrations for komatiite basalt lava sequences of the kostomuksha greenstone belt and for the komatiite standards kal 1 abitibi and wits 1 barber ton the flowtop breccia komatiites mgo 5 27 5 from the kostomuksha sequence which represent the composition of the primary komatiite liquid have os 5 1 5 6 0 1 ppb chondritic os ir n 5 1 06 6 0 05 and moderately fractionated pge patterns pd os n 5 6 5 6 0 4 based on the kal 1 standard the alexo primary liquid had os 5 1 8 6 0 1 ppb os ir n 5 1 05 6 0 05 and pd os n 5 8 5 6 1 0 pges in the kostomuksha komatiites exhibit incompatible behavior during magmatic differentiation with bulk d values of os ir 5 0 75 pt 5 0 52 and pd 5 0 pge abundances from kostomuksha komatiites and basalts were used to calculate the pt os and re os composition of a magnesian archean oceanic crust the pt re os isotopic evolution of this crust was modeled indicating that coupled 186 187 os enrichments observed in some modern plumes require a non crustal source a previously proposed model for core mantle interaction by physical admixture was evaluated and was shown to produce mantle sources with high pge abundances os 5 6 to 14 ppb pd 5 140 ppb for 1 outer core addition and os ir n 1 depending on the assumptions made these features were not observed in the kostomuksha komatiites g 187 os t 51 3 6 shown here to be derived from a reservoir with 25 lower absolute pge abundances than primitive mantle if the radiogenic initial 187 os 188 os in the kosto muksha komatiite is an outer core signature then core mantle interaction cannot have involved physical admixture of outer core material into mantle plume sources instead it must have occurred in the form of isotopic equilibration between liquid outer core and solid mantle at the core mantle boundary copyright 2000 elsevier science ltd

osmium and neodymium isotopic constraints on the temporal and spatial evolution of siberian flood basalt sources high mg volcanic rocks from the ca 250 ma old siberian flood basalt province sfbp were analyzed for their osmium and neodymium isotopic compositions in order to help to constrain source characteristics as the system evolved picrites from the gudchikhinsky suite the oldest rocks examined have os of 5 3 to 6 1 and nd of 3 7 to 4 0 the osmium and neodymium isotopic compositions of these rocks are similar to some modern ocean island basalts oib consistent with their derivation from a mantle plume and show little evidence for interaction with either subcontinental lithospheric mantle sclm or the precambrian siberian craton through which the parental melts passed picrites from the stratigraphically higher tuklonsky suite have similar os of 3 4 to 6 5 but nd of 0 9 to 2 6 the similar os but lower nd for the tuklonsky picrites as compared with the gudchikhinsky picrites suggest that some magmas from the same oib type mantle source were contaminated by lithospheric components the osmium isotopic composition of the tuklonsky picrites was not significantly affected by this interaction possibly because os concentrations in the magmas were substantially greater than those in the contaminant a differentiated ankaramite flow associated with the top of the stratigraphically higher morongovsky suite has os of 9 8 to 10 2 and nd of 1 3 to 1 4 the higher os may indicate that the plume source was heterogeneous with respect to osmium isotopic composition consistent with osmium isotopic measurements in rocks from other plume sources in contrast to these rocks mg rich alkaline rocks meymechites from the guli area that erupted much nearer the end of the flood basalt event have os of 1 2 to 2 6 and nd of 3 7 to 4 9 these rocks were probably produced by low degrees of partial melting of mantle after the main stages of flood basalt production the relatively low os and high nd for the meymechites together with a variety of trace element characteristics are most consistent with derivation from a mixed source one that included both the 0113 type source that fed the majority of the flood basalt system and a major component from the sclm underlying the siberian craton these results taken together with earlier investigations of the noril sk type ore bearing intrusions suggest that much of the sfbp consists dominantly of plume derived material until relatively late in the magmatic event when the sclm became a significant source of material

evolution and origin of deep reservoir water at the activo luna oil field gulf of mexico mexico petroleum wells of the activo de produccion luna oil field at the mexican gulf coast are partially invaded by formation water at a production depth between 5000 and 6000 m measured 14c activities between less than 0 9 and 13 7 modern carbon reflect a homogenous late pleistocene early holocene age 40 10 ka for the regional infiltration of meteoric and marine water into the reservoir before infiltration both components were partially affected by atmospheric evaporation which explains the hypersaline composition of some formation waters very positive d18o values up to 12 5 of the formation waters are caused by strong secondary water rock interaction processes and reflect close to equilibrium conditions between the carbonate host rock and the fluids the formation of biogenic and or thermocatalytic methane in some parts of the petroleum reservoir is indicated by d13c values up to 20 4 southwest northeast directed hydraulic migration of the deep aquifer between camps sen and escuintle pijije caparroso is indicated by interference tests and pressure drawdown characteristics whereas northwest southeast trending thrust faults restrict communication toward the luna and tizon camps in the most northeastern part of the oil field on a local scale vertical zonation trends of the fluids with decreasing salinity toward upper parts of the common aquifer are related to separation processes by gravity and or by the rising of condensed vapor the migration of the fluids is mainly related to southwest northeast trending fractures and microfractures whereas northwest southeast and northeast southwest trending reverse and normal faults respectively behave irregularly as barrier or as flow conduits recently the extraction of petroleum caused an increased mobilization of the hydrodynamic aquifer system begin page 458

platinum group minerals in alpine chromitites from southwestern oregon electron microprobe and scanning electron microscopy the platinum group minerals found in the chromitites are laurite porous ru rich alloys os ir and pt rich alloys with highly variable compositions an ir cu rich sulfide a pt arsenide and three relatively rare platinum group sulfides the platinum group minerals are 1 to 30 mu m in diameter and occur as inclusions in chromite grains some of these inclusions also contain silicates and millerite base metal alloys largely ni fe occur in cracks in the chromitites along with magnetite ferritchromite chromian chlorite and serpentine the primary platinum group mineral assemblage is interpreted to have formed before or during crystallization of the chromite grains and not as a result of exsolution from the chromite modified journal abstract

pge distribution in 2 7 ga layered komatiite flows from the belingwe greenstone belt zimbabwe the well preserved anderson s and onias s komatiite flows from the late archaean belingwe greenstone belt 2 7 ga zimbabwe were sampled in the saskmar drill hole anderson s flow possesses a 1 1 m thick b1 subzone and a clinopyroxene spinifex subzone whereas onias s flow has spinifex and cumulate layers typical of komatiite flows platinum group element pge abundances throughout these two flows provide constraints on the formation of layered komatiite flows all samples from both flows have similar chondrite normalized pge patterns that are enriched in rh pt and pd relative to os and ir which are attributed to large degrees 30 of partial melting of the upper mantle their pd ir ratios are highly variable 2 0 31 in onias s flow and 2 3 61 in anderson s flow pge variations within both flows except the spinifex a zone and b1 subzone of anderson s flow together with those of major and other trace elements are consistent with a model involving olivine fractionation the spinifex a zone of anderson s flow has low pd ir ratios 6 8 which occur in an interval having negative eu anomalies caused by hydrothermal alteration the pt fractionation from pd and rh is documented from their relationship to mgo contents behaviours of pd and rh are similar and more incompatible than pt at the early stage of relatively slow cooling but less incompatible at the late stage during the formation of komatiite flows pge in the b1 subzone of anderson s flow do not follow an olivine fractionation trend pd ir ratios in this subzone increase from 28 at the top to 61 at the base these unusually high values can be accounted for by late stage development of the subzone and strong fractionation

platinum group element fractionation in a komatiitic basalt lava lake precise pge os ir ru pt pd abundance data for bulk rock samples and mineral separates from a deep differentiated komatiitic basalt lava lake in the vetreny belt baltic shield were obtained using an icp ms id technique the composition of the erupted liquid mgo 5 15 is characterized by a highly fractionated pge pattern pd os n 5 48 with subchondritic os ir n 5 0 43 analysis of separated olivine and chromite revealed that ru os and ir were slightly compatible to moderately incompatible in olivine d 5 1 7 0 8 and were compatible with chromite d 5 100 150 platinum and pd were highly incompatible with olivine d 5 0 08 0 03 and moderately compatible with chromite d 5 1 6 3 3 bulk solid liquid partition coefficients for pges ni cr and cu estimated from the whole rock regressions were os 7 9 ir 6 6 ru 4 5 pt 0 53 pd 0 09 ni 6 2 cr 4 4 and cu 0 01 the highly incompatible behavior of cu and pd indicates that there was no separation of fenicu immiscible sulfide liquid during the differentiation of the lava lake comparison of the bulk partition coefficients with those calculated from the olivine and chromite compositions implies that the fractionating mineral assemblage included 10 2561 mass fraction of pyrrhotite the data obtained provide new constraints on the effects of fractional crystallization on the pge compositions of mafic ultramafic magmas copyright 2001 elsevier science ltd