waveform inversion for one dimensional near surface structure in the new madrid seismic zone waveform inversion is applied to p and s waveforms selected from microearthquakes of duration magnitude m d between 1 8 and 2 4 recorded at station parm in stahl farm missouri operated by the cooperative new madrid seismic network in the upper mississippi embayment to resolve the one dimensional 1d velocity structure of uppermost near surface soils constrained by vertical seismic profiling vsp and standard cone penetration test scpt data at nearby sites we begin by defining a gradient velocity structure in the soils a reference velocity model is constructed by grid search in which the observed p and p s wave shapes graphic 1 travel time and p p s amplitude ratio are the controlling factors in the systematic selection from among 136 000 models a waveform inverse scheme is then implemented to obtain the least spectral misfit and best waveform correlation between synthetic and observed data four simultaneous inversions of joint waveforms from p and s wave types are performed resolved four 1d final models with associated uncertainties are listed in this article the uppermost 7 m of near surface soil exhibit very low velocities through which v p and v s are in the ranges of 140 m s to 470 m s and 95 m s to 215 m s respectively this noninvasive technique demonstrates that the observed high frequency reverberations 1 17 hz of p s and p s waveforms from local microearthquakes can be utilized to provide a view of the near surface soil structure although there are trade offs between layer thickness and slowness this method explains much of the high frequency site response due to microearthquake wave propagation through the very low velocity near surface soils 1 embed inline graphic 1 gif

sulfur isotope exchange and metal enrichment in the formation of magmatic cu ni pge deposits sulfur isotope measurements provide a useful means of evaluating the source of sulfur in magmatic cu ni pge deposits although low sulfur pge rich deposits e g j m reef of the stillwater complex merensky reef of the bushveld complex show little or no isotopic evidence for the involvement of crustally derived sulfur several high sulfur deposits e g noril sk duluth complex show strong evidence for contamination of mafic magmas by sulfur of crustal origin processes such as magma degassing or redox changes accompanying crystallization are ineffective in significantly modifying sulfur isotope signatures of sulfides that crystallize from immiscible liquids that exsolve from the mafic magmas for this reason 34s values are primarily dependent on sulfur source characteristics and variations can often be treated using a two component mixing approach however deposits such as those at noril sk and voisey s bay that appear to have formed in magma conduit systems present another possibility for modification of sulfur isotope signatures these deposits are thought to have been upgraded in metal tenor by reaction with uncontaminated mantle derived melts that traversed the accumulated sulfide on their way to the surface our calculations illustrate the efficiency of reactions that involve the exchange of fe for cu ni or pge in producing increases in the metal tenor of the accumulated sulfide sulfur isotope exchange between the crustally contaminated sulfide ore accumulation and sulfur of mantle origin may accompany chalcophile element exchange and is capable of masking or limiting the degree of isotopic evidence for the initial stage of ore genesis that involved crustal sulfur sulfur isotope exchange is distinct from the addition of sulfur in the form of immiscible sulfide droplets from a sulfide saturated magma to the accumulated sulfide although both additive mixing and exchange can lead to similar isotopic effects stable isotopic exchange provides a mechanism in addition to additive mixing that may lead to decoupling of different isotopic systems

world class ni cu pge deposits key factors in their genesis magmatic ni cu sulfide deposits form as the result of segregation and concentration of droplets of liquid sulfide from mafic or ultramafic magma and the partitioning of chalcophile elements into these from the silicate melt sulfide saturation of a magma is not enough in itself to produce an ore deposit the appropriate physical environment is required so that the sulfide liquid mixes with enough magma to become adequately enriched in chalcophile metals and then is concentrated in a restricted locality so that the resulting concentration is of ore grade the deposits of the noril sk region have developed within flat elongate bodies 15 2 0 2 km that intrude argillites evaporites and coal measures adjacent to a major trans crustal fault and immediately below the centre of a 3 5 km thick volcanic basin studies of the overlying basalts have shown that lavas forming a 500 m thick sequence within these have lost 75 of their cu and ni and more than 90 of their pge overlying basalts show a gradual recovery in their chalcophile element concentrations to reach normal values 500 m above the top of the highly depleted zone the ore bearing noril sk type intrusions correlate with those basalts above the depleted zone that contain normal levels of chalcophile elements the high proportion of sulfide 2 10 wt associated with the noril sk type intrusions the high pge content of the ores the extensive metamorphic aureole 100 400 m around the bodies and the heavy sulfur isotopic composition of the ores 8 12 34s are explicable if the ore bearing bodies are exit conduits from high level intrusions along which magma has flowed en route to extrude at surface the first magma to enter these intrusions reacted with much evaporitic sulfur at a low r value and thus gave rise to sulfides with low metal tenors successive flow of magma through the system progressively enriched the sulfides in the conduits losing progressively less of their chalcophile metals and thus accounting for the upward increase in metals in successive lava flows above the highly depleted flows the voisey s bay deposit lies partly within a 30 100 m thick sheet of troctolite interpreted as a feeder for the 1 334 ga voisey s bay intrusion and partly at the base of this intrusion where the feeder adjoins it studies of olivine compositions indicate that an early pulse of magma through the feeder and into the intrusion was ni depleted but that subsequent pulses were much less depleted trace element re os and s and o isotope data and mineralogical studies indicate that the magma pulses interacted with country gneiss probably principally in a deeper level intrusion extracting sio2 na2o k2o and possibly sulfur form the gneiss which accounts for the magma becoming sulfide saturated the jinchuan deposit of north central china occurs within a 6 km long dyke like body of peridotite the compositions of olivine within the dyke the igneous rocks themselves and the ore are all inconsistent with derivation of the body from ultramafic magma as originally supposed and indicate that the structure forms the keel of a much larger intrusion of magnesian basalt magma flow of magma into the intrusion has resulted in olivine and sulfide being retained where the keel was widening out into the intrusion the west australian komatiite related deposits occur in thermal erosional troughs which have developed due to the channelisation of magma flow and the resulting thermal erosion of underlying sediments and basalt by the hot komatiite magma the sediments are sulfide rich and may have contributed substantially to the sulfide of the ores the mineralisation in the duluth complex occurs in troctolitic intrusions along the western margin of the complex as a result of magma interacting with and extracting sulfur from the underlying graphite and sulfide bearing sediments no magma flow channels have been identified so far and the lack of magma flow subsequent to the development of sulfide immiscibility is regarded as the reason why these deposits are not of economic grade when most major ni cu sulfide deposits are compared they prove to have a number of features in common olivine rich magma proximity to a major crustal fault sulfide bearing country rocks chalcophile element depletion in related intrusive or extrusive rocks field and or geochemical evidence of interaction between the magma and the country rocks and the presence of or proximity to a magma conduit the features are thought to explain the three key requirements sulfide immiscibilty adequate mixing between sulfides and magma and localisation of the sulfides discussed and have important implications with respect to exploration

36cl as a tracer in geothermal systems example from valles caldera new mexico the chlorine 36 content of three thermal waters from valles caldera new mexico has been analyzed to investigate the use of chlorine 36 as a geothermal tracer

imaging shallow crustal structure in the upper mississippi embayment using local earthquake waveform data a 1d normal moveout nmo corrected and stacked pseudoprofiling method was applied to analyze the characteristic features shown on primary p and s wave coda and on sp waveforms from local microearthquakes in an attempt to image prominent reflectors and to resolve shallow crustal velocity structure 5 km in the upper mississippi embayment acoustic well log data were used to constrain the p wave velocity in the upper 5 km events at close distances and with clear p and s arrivals were selected to ensure reliable nmo correction for reflections and transmissions the observed reflections and transmissions are important controlling factors on modeling waveforms we analyzed local earthquake data recorded at all broadband and one short period station of the cooperative new madrid seismic network despite polarity differences among p s and sp waveforms consistent reflectors in the sedimentary section can be imaged across the three wave types correlation with a basement penetrating well indicates that reflectors at the base of the upper cretaceous holocene mississippi embayment supergroup the base of the cambrian ordovician knox group and the high velocity lower upper cambrian bonneterre formation are shown in pseudoprofiles among stations in the upper mississippi embayment our study finds that a one layer homogeneous velocity model of sediments in the ranges of 1 95 2 42 km s for v p and 0 60 0 73 km s for v s overlying a half space of paleozoic rocks with velocities in the ranges of 6 0 6 2 km s for v p and 3 26 3 6 km s for v s can represent shallow crustal structure in the upper mississippi embayment differential times of p ppphp and s ssshs appear linearly proportional to sediment thicknesses which best fits a one layer sediment structure with average v p 2 042 0 041 km s and v s 0 709 0 051 km s in the least squares sense predicted by the wave propagation effects online material figures illustrating seismograms process procedure imaged reflectors and resolved velocity structure for six broadband stations and one short period station

geochronology of an archaean tonalitic gneiss dome in northern finland and its relation with an unusual overlying volcanic conglomerate and komatiitic greenstone archaean gneiss greenstone relationships are still unresolved in many ancient cratonic terrains although there is growing evidence that most of the late archaean greenstone assemblages were deposited on older tonalitic crust

local earthquake wave propagation through mississippi embayment sediments part ii influence of local site velocity structure on qp qs determinations elastic near surface structure and receiver depth effects are seen to control body wave amplitude spectra in the band from 2 to 50 hz for local earthquake observations in the new madrid seismic zone p and s wave spectral peaks are created by resonance in shallow low velocity zones and spectral nulls are created by interference of direct and free surface reflections due to receiver depth these wave propagation effects dominate sp s spectral ratios and mimic anelastic attenuation effects by making it appear that s waves are deficient in higher frequencies relative to sp waves there is no evidence from sp s spectral ratios that unconsolidated sediments of the mississippi embayment are highly attenuating dominance of p and s wave resonance suggests that the unconsolidated sediments amplify rather than attenuate seismic waves at high frequency this has important implications for estimating hazards from strong ground motions in the area in the absence of any identifiable anelastic attenuation effect in the spectral ratio the only allowable q p q s relationship for embayment sediments is that q s 3 q p based on consideration of wave travel times manuscript received 11 march 2003

hydrothermal transport of ag au cu pb te zn and other metals and metalloids in new zealand geothermal systems spatial patterns fluid mineral equilibria and implications for epithermal mineralization in order to analyze the concentrations of ag as au cd cu hg mn mo ni pb se sb te tl w and zn in deep hydrothermal chloride waters at 195 to 320 c and in shallow boiled chloride waters at 160 to 230 c we sampled wells drilled to 3 km depth in geothermal systems of the north island new zealand six of the systems are located in a segment of volcanic arc in the central taupo volcanic zone and the seventh system is associated with an intraplate mafic felsic volcanic center the concentrations of metals range widely from 0 1 to 1 000 g kg with a large degree of intersystem variability some of the largest contrasts in au ag pb and te concentrations are observed in the two nearest systems rotokawa and wairakei which are only 10 km apart the correlations between metals are poor except for ag au pb te and as sb the correlations between metals cl and h2s are also poor with the exception of rotokawa where the highest concentrations of ag au cu and te correlate with the highest concentration of aqueous h2s speciation calculations indicate that the dominant aqueous species of ag au cu pb and zn involve hs complexes the calculations also show that the states of saturation range from undersaturated conditions for acanthite arsenopyrite and gold to oversaturated conditions for chalcopyrite sphalerite and tellurides notably the au and ag transporting capacities of the deep chloride waters are much larger than the measured aqueous concentrations these results suggest that fluid mineral equilibria and the concentrations of ligands exert weak influence on metal concentrations at the temperatures and depths of sampling the complex trends in hydrothermal metal concentrations strongly suggest that the deep seated sources of metals comprising magmatic intrusions deep country rock and their related fluids limit the hydrothermal supplies of metals between the geothermal systems hydrothermal fluxes of ag 6 8 000 kg y au 0 9 66 kg y cu 30 23 500 kg y and te 2 10 400 kg y are variable the highest concentrations and fluxes of ag au and te in rotokawa and mokai are attributed to direct fluid inputs from intrusions of andesitic and basaltic magmas respectively compared to their deep counterparts boiled chloride waters are strongly depleted in ag au cd cu pb and te because these metals deposit in sharp response to gas loss and cooling in the well by comparison the as mn mo ni sb tl and zn concentrations are measurably less depleted in boiled waters making them available to form metal anomalies at shallow depths and in the peripheral parts of the epithermal environment periods of strong metal flux through the geothermal system combined with deep boiling favor epithermal ore formation and the development of large precious metal deposits however even moderate metal fluxes can produce au and ag mineralization as long as the duration of focused fluid flow and boiling can be sustained there is no evidence that the compositions of deep magmatic intrusions mafic or intermediate limit the ore forming potential of a geothermal system

chemical and isotopic signature of old groundwater and magmatic solutes in a costa rican rain forest evidence from carbon helium and chlorine 1 c he and cl concentrations and isotopes in groundwater and surface water in a lowland costa rican rain forest are consistent with the mixing of two distinct groundwaters 1 high solute bedrock groundwater representing interbasin groundwater flow igf into the rain forest and 2 low solute local groundwater recharged in the lowlands in bedrock groundwater high 13c 4 89 low 14c 7 98 pm high r ra for he 6 88 and low 36cl cl 17 10 15 suggest that elevated tracer concentrations are derived from magmatic outgassing and or weathering of volcanic rock beneath nearby volcan barva in local groundwater the magmatic signature is absent and data suggest atmospheric sources for he and cl and a biogenic soil gas co2 source for dissolved inorganic carbon dating of 14c suggests that the age of bedrock groundwater is 2400 4000 years most likely at the lower end of the range local groundwater has 14c 100 pm indicating the presence of bomb carbon and thus ages less than 55 years overall data are consistent with a conceptual hydrologic model originally proposed on the basis of water budget and major ion data 1 large variation in solute concentrations can be explained by mixing of the two distinct groundwaters 2 bedrock groundwater is much older than local groundwater 3 elevated solute concentrations in bedrock groundwater are derived from volcanic fluids and or rock and 4 local groundwater has not interacted with volcanic rock tracers with different capabilities converge on the same hydrologic interpretation also transport of magmatic co2 into the lowland rain forest via igf seems to be significant relative to other large ecosystem level carbon fluxes

129i and 36cl in dilute hydrocarbon waters marine cosmogenic in situ and anthropogenic sources abstract the long lived halogen radioisotopes 129 i and 36 cl provide valuable information regarding the source of fluids in hydrocarbon systems and in localized areas where infiltration of younger meteoric water has occurred despite the utility of these two isotopes in providing time signatures for fluid end members considerable uncertainty remains regarding the interpretation of intermediate age waters in hydrologic systems these waters are likely the result of the combination of two or more halogen sources at some time in the past each with its own characteristic concentration and isotopic composition in order to unravel the evolution of these intermediate age waters the effect that infiltration of meteoric water has on the isotopic composition of older formation waters is modeled also evaluated is the effect that the timing of dilution has on 129 i and 36 cl signatures observed in the present specifically the hypothesis that halogen isotopic signatures imparted by the mixing of brine and meteoric waters early in the development of a sedimentary basin are quantitatively different from those imparted by the mixing of old brines with recent meteoric waters the modeled results are compared to previously published isotopic data from production wells in the fruitland formation coalbed methane system portions of the basin preserve enough of the original brine source to retain 129 i i ratios roughly recording the age of deposition of organic matter 73 76 ma even where some degree of dilution by meteoric water has occurred however the 129 i signatures of waters that presently contain less than 10 of the original formation water component indicate that mixing has occurred within the past 10 ma consistent with recently published 4 he data both 36 cl concentrations and 36 cl cl ratios show that waters containing more than 10 formation water are all in secular equilibrium with the host formation coals in contrast waters with less than 1 of the original formation water s cl content all have 36 cl cl ratios which are greater than secular equilibrium values indicating the migration of meteoric water into the coal formation more recently than 2 ma although 36 cl signatures in the fruitland formation are not significantly affected by anthropogenic input 129 i i ratios in a subset of samples that retain less than 1 of the initial formation water component suggest input of anthropogenic 129 i during the past 50 a

geotechnical site characterization in the greater memphis area using cone penetration tests abstract the determination of seismic ground hazards in memphis and shelby county tennessee is facilitated by the use of electronic cone penetration tests that can provide up to four independent readings with depth from a single sounding one series of soundings is being performed for site specific mapping to determine the presence and extent of potentially liquefiable sediments in situ soil resistance to liquefaction and initial soil stiffness for ground motion amplification studies another series of soundings is being conducted in conjunction with field paleoliquefaction mapping in the new madrid seismic zone to better define the intensity magnitude and geographic extent of ground failures caused by large past earthquake events as well as information about the source sands in this paper an overview is given on the types of multi channeled penetrometer data that are being collected including vertical profiles of cone tip stress qt sleeve friction fs penetration porewater pressure u1 or u2 downhole shear wave velocity vs and or electrical conductivity ke representative soundings are presented from select sites to illustrate repeatability data post processing methods and that derived downhole vs profiles are generally in good agreement with non invasive surface techniques at two memphis test sites cyclic stress based procedures for liquefaction are discussed with relation to data from a paleoliquefaction site in germantown tennessee and estimates of the minimum magnitude of the historic event are discussed while estimates of the earthquake magnitude are preliminary pending additional study on attenuation relationships and site response in the deep soils of the mississippi embayment it is inferred from evaluation of in situ test data using cyclic stress based techniques that the december 1811 new madrid earthquake was likely larger than a mw 7 5 event

local earthquake wave propagation through mississippi embayment sediments part i body wave phases and local site responses p and s body waves from microearthquakes in the new madrid seismic zone nmsz are investigated at selected sites in an effort to understand wave propagation from future large earthquakes earthquake body waveforms display distinctive features that constrain the nature of p and s wave local site responses and wave propagation within the unconsolidated mississippi embayment sediments modeling of the waveforms demonstrates that a near surface low velocity zone is characteristic of structure within the upper 60 m of the sedimentary column and produces large p and s wave resonance effects that can be used to infer near site conditions site resonance effects change because of velocity heterogeneity between individual receivers but imply that embayment sediments will substantially amplify ground motions at high frequencies site resonance affects p and s wave amplitude spectra and can bias estimates of source and anelastic attenuation parameters travel times of observed body wave phases such as p ppphp the first p wave reverberation within the entire sedimentary column ps sp s and ssphp can be used to estimate the average wave slownesses and poisson s ratio within the embayment sediments an average poisson s ratio of 0 44 is obtained for the central nmsz under station pebm detailed s wave velocities are derived for a nafe drake sediment model using acoustic well logs and the travel time constraints of observed seismic phases v p v s ratios vary from 5 5 near the surface to approximately 2 4 at the base of the sediments use of the well log data in wave calculations also explains much of the nature of p and s wave coda within the waveforms and shows that 1d heterogeneity is a first order influence on seismic wave propagation within the mississippi embayment manuscript received 11 march 2003

insights into ore genesis of ni cu pge sulfide deposits of the noril sk province russia evidence from copper and sulfur isotopes abstract combined cu s isotope data for ni cu pge sufides from the economic deposits hosted in the noril sk 1 talnakh and kharaelakh intrusions from the subeconomic deposits in the chernogorsk zub marksheider and vologochan intrusions and from the non economic occurrences in the nizhny talnakh intrusion in the noril sk province russia and the j m reef in the stillwater complex usa are presented for the first time most sulfide samples including the ores from the talnakh intrusion and the stillwater complex have a restricted range of 65 cu values from 1 1 to 0 whereas those from the kharaelakh and noril sk 1 intrusions have more variable 65 cu values of 2 3 to 1 0 samples from the three economic deposits in the noril sk province have distinct mean 65 cu values of 1 56 0 27 for kharaelakh 0 55 0 41 for talnakh and 0 23 0 28 for noril sk 1 consistent with those for carbonaceous chondrite and iron meteorites the variation of 65 cu values is interpreted to represent a primary signature of the ores although a magmatic fractionation of cu isotopes and or assimilation from an external source cannot be ruled out particularly in the case of the kharaelakh ores collectively the eight investigated intrusions have an overall sulfur 34 s range from 0 7 to 13 8 disseminated and massive ores of the same intrusion have similar 34 s values the disseminated and massive ores of the khraelakh intrusion have a mean 34 s value of 12 57 0 54 and 12 76 0 42 respectively which are distinctly different from those of the disseminated 10 97 0 44 and massive ores 10 88 0 77 of the talnakh intrusion the different 34 s values of the intrusions may be attributed to sulfur fractionation in deep seated magma chambers rather than at shallow levels or the present emplacement site the mean 34 s value of the disseminated ores from the subeconomic ni cu pge deposits and non economic occurrences spans over 10 5 averaging 0 39 with a standard deviation of 1 55 for the highly contaminated zub marksheider rocks 6 38 1 89 for nizhny talnakh 6 90 1 17 for vologochan and 10 86 0 43 for chernogorsk samples from the zub marksheider intrusion have mantle like s isotope signatures consistent with a deep seated origin although individual mineralized instrusions have a restricted range the overall trend they define of falling 34 s with rising 65 cu values might be a useful indicator of the economic potential of ni cu pge sulfide deposits

late cretaceous and cenozoic geology of the new madrid seismic zone structure contour maps constructed from well seismic reflection and outcrop data of the tops of the paleozoic section upper cretaceous section paleocene midway group and eocene section illustrate the post paleozoic structure of the new madrid seismic zone region isopach maps of the late cretaceous section midway group and eocene section help constrain the timing of the structural events these maps which encompass much of the northern mississippi embayment reveal reactivation of the underlying late precambrian cambrian reelfoot rift during midway group deposition but no reactivation during late cretaceous or eocene deposition the structure contour maps also indicate a subtle south plunging depression on the tops of the paleozoic upper cretaceous and midway group along the axis of the northern mississippi embayment that we have called a trench this trench is 50 km wide has a maximum depth of 100 m and appears to have formed during the eocene the trench s western boundary coincides with the blytheville arch lake county uplift and its southeastern margin underlies memphis tennessee the blytheville arch lake county uplift is the structure responsible for the new madrid seismic zone and thus it is possible that the southeastern margin of the trench is also a fault zone northern mississippi embayment post paleozoic stratigraphy consists of sands silts and clays that thicken from 477 m at new madrid missouri to 987 m near memphis tennessee the uniformity of these sediments indicates their elastic properties and therefore seismic velocities are very similar however variations in cementation and unconformities within the section may influence seismic wave propagation manuscript received 17 june 1999

seismic imaging of the site response using microearthquake recordings part i method abstract microearthquake signals from widely distributed geographical regions have been noticed repeatedly to be strongly affected by local site effects the corresponding seismograms contain important information on the individual propagation path a single station inversion method is presented which allows the imaging of the subsurface impedance structure from locally recorded sh waves records the technique is based on the kunetz claerbout equation which in its original form states the relationship between the transmission response and the reflection response for p waves in a horizontally layered medium and vertical incidence claerbout 1968 by adapting claerbout9s formulation to the transmission problem for sh waves under oblique incidence microearthquake recordings can be used to calculate corresponding pseudo reflection seismograms which in turn can be inverted for the impedance structure by exploiting levinson recursion limitations in the high frequency content of the signals due to the combined effects of absorption recording system and bandlimited source signals as well as the influence of noise drastically reduce the resolutional power of the inversion procedure a number of different deconvolution techniques have been tested with synthetic seismograms for the applicability to reduce these effects good results have been obtained with the blind deconvolution technique of scherbaum and stoll 1985 utilizing the minimum phase property of the green9s function from the analysis of synthetic data it can be expected that for realistic source receiver situations and short period recording systems the main reflectors down to a depth of several hundreds of meters could be resolved

infiltration metasomatism in layered intrusions an example from the stillwater complex montana abstract the contact between anorthosite zone ii an ii and the overlying troctolite of olivine bearing zone v ob v of the stillwater complex is characterized by a 5 m thick adcumulate anorthosite this adcumulate anorthosite separates rocks of an ii characterized by the apparent crystallization sequence plagioclase followed by orthopyroxene clinopyroxene quartz fe ti oxide assemblages from those of ob v where the apparent crystallization sequence is olivine plagioclase followed by orthopyroxene the grain size and compositional zoning of plagioclase in this transition zone is similar to that in the overlying troctolite and distinct from the coarser complexly zoned plagioclase that makes up the underlying anorthosite in contrast the minor interstitial pyroxene in the transition zone compositionally overlaps that in the underlying anorthosite and both have a lower molar mg mg fe ratio than the pyroxene of the troctolite these relationships suggest that the intercumulus liquids of an ii and ob v were compositionally distinct model phase diagram considerations suggest that infiltration of any plagioclase saturated liquids into a troctolite assemblage will result in the assimilation of olivine and depending on the actual composition of the anorthositic liquid will also either assimilate or crystallize plagioclase as well hence the monomineralic anorthosite zone at the top of an ii can be attributed to infiltration of interstitial liquids from an ii that were displaced upward into the troctolite during compaction of an ii this reaction can be either exothermic or endothermic depending on the actual composition of the infiltrating liquid and the bulk solids composition numerical models of the thermal effects of infiltration suggest that heat of reaction can significantly affect the liquid solid ratio away from the infiltration boundary

microtremor observations of deep sediment resonance in metropolitan memphis tennessee we measured site resonance periods throughout metropolitan memphis tennessee the site resonance was derived from recordings of ambient microtremor and is a direct measurement of seismic ground shaking in the memphis metropolitan area the period t0 in s is predicted by the empirical relation t0 0 39899 7 8922 10 3h 3 0634 10 6h2 350 h 1100 m where h is the thickness in m of the unconsolidated sediments that overly hard paleozoic rocks assuming that a quarter wavelength relationship governs the relationship between resonant period sediment thickness and average shear wave speed we estimate the average shear wave speed of unconsolidated sediments as a function of sediment thicknesses vs 521 15 0 37459h 350 h 1100 m the scatter in the observations and discordance with earlier work suggests that caution is warranted in applying these values of wave speed indiscriminately to sites in the absence of further detailed work

a cocorp deep reflection profile across the buried reelfoot rift south central united states abstract a cocorp deep reflection survey across the northern mississippi embayment reveals essential features of the late precambrian early paleozoic reelfoot rift stratified reflections delineating the sedimentary fill of the rift basin are of variable thickness the base ranging from 2 0 to a maximum of 3 5 s twt 4 to 8 km depth in contrast the base of phanerozoic the sedimentary section immediately east of the rift is at 1 4 s 2 8 km depth correlation with a basement penetrating well indicates that the base of the upper cretaceous holocene mississippi embayment supergroup base of the cambrian ordovician knox group and the lower upper cambrian bonneterre formation are basin wide seismic stratigraphic markers clastic sedimentary strata of the lamotte formation which immediately overlie precambrian basement show clear angular discordance with the overlying subhorizontal bonneterre formation indicating that the base of the bonneterre marks the transition from active extension to passive subsidence within the reelfoot rift palinspastic restoration of the basement suggests relatively modest extension associated with rift formation 17 the blytheville arch an axial antiformal feature as well as a number of lesser structures indicative of multiple episodes of fault reactivation are also evident on the cocorp profile the crystalline basement beneath the reelfoot rift is relatively devoid of reflections down to 5 0 s 12 15 km depth beyond which it passes gradationally into a complexly reflective diffractive middle and lower crust the lower crust however does not exhibit the distinctly laminated character commonly observed in mesozoic cenozoic extensional provinces the crust mantle transition beneath the rift is characterized by a gradational downward cessation of crustal reflectivity at 12 13 s 40 km depth followed by an unreflective zone which in turn is followed by a distinct horizontal reflection at 14 5 s the latter is not observed on existing profiles outside the rift at present it is not possible to determine strictly whether the deep horizon represents moho or alternatively a discrete feature sill within the uppermost mantle however its spatial association with the reelfoot rift suggests that the two are genetically related regional relations together with the existence of dipping fabric in the deep crust beneath the rift suggest the possibility that the reelfoot rift formed along the southern extension of the circa 1 ga grenville front

origin of ultra nickeliferous olivine in the kevitsa ni cu pge mineralized intrusion northern finland the 2 058 4 ma mafic ultramafic kevitsa intrusion is located in the central lapland greenstone belt northern finland it is hosted by a paleoproterozoic volcano sedimentary sequence that contains komatiitic volcanic rocks and sulfide and graphite rich black schists economic ni cu pge sulfide mineralization occurs in the middle part of the ultramafic lower unit of the intrusion two main types of ore are distinguished normal and ni pge ores the normal ore is characterized by 2 to 6 vol disseminated sulfides and average ni and cu grades of 0 3 and 0 42 wt respectively ni cu 1 the ni pge ore has broadly similar sulfide contents but a higher ni grade and lower cu grade as a result the ni cu ratio reaches 15 much higher than in the normal ore the ni pge ores occur as irregular discontinuous lense like bodies in the ultramafic rocks notably the olivines in the ni pge ore contain extremely high ni contents of up to 14 000 ppm which is significantly higher than the ni content of olivine in other mafic ultramafic igneous rocks globally up to 5 000 ppm and in harmony with the associated ni rich sulfide assemblage containing pentlandite millerite and pyrite microprobe mapping of olivine from the ni pge ore suggests relatively low and homogeneous s contents and homogeneous distribution of ni mg fe which is inconsistent with the presence of sulfide inclusions in the olivine grains or diffusion of ni from interstitial sulfides into the olivine grains we therefore conclude that ni substitutes for mg in the olivine lattice the clinopyroxenes from the ni pge ore also have unusually high ni concentrations reaching 1 500 ppm and show a positive correlation with the nickel content of the associated olivine the nicpx niolivine is 0 1 to 0 2 corresponding to high t partitioning of ni between clinopyroxene and olivine k d of 20 can account for the partitioning of nickel between olivine and the sulfide phase consistent with magmatic equilibration these data suggest that the olivine clinopyroxene and sulfides all crystallized from a basaltic magma with an unexceptionally high ni content ranging from 300 to 1 100 ppm the ni pge ores are spatially associated with ultramafic xenoliths olivine in these ultramafic xenoliths have relatively high fo contents up to 90 mol and high ni contents up to 5 200 ppm suggesting that the xenoliths formed from a komatiitic parental magma it is proposed that assimilation by the kevitsa magma of massive or semi massive sulfides associated with komatiitic rocks elevated the ni content of the magma and resulted in the formation of ni pge ores and related extremely ni rich olivines

mineral compositional constraints on petrogenesis and oxide ore genesis of the late permian panzhihua layered gabbroic intrusion sw china a systematic study of mineral compositions has been carried out on stratigraphic sections through the panzhihua intrusion a layered gabbroic sill of late permian age that hosts significant magmatic fe ti v oxide deposits in the emeishan large igneous province sw china the intrusion which is 19 km long and 2 km thick is divided into a marginal zone mgz lower zone lz middle zone sub zones mza and mzb and upper zone uz from the base upwards compositions of the most primitive cumulus olivine fo81 and plagioclase an73 found in the intrusion suggest that the parental magma was similar to the mg rich end member of the coeval high ti basalts in the region two reversals in terms of mineral compositions are found in the intrusion one in the lower mza and the other at the transition between the mzb and the uz the first reversal is marked by a gradual increase in the an content of plagioclase an60 to an70 over a 100 m vertical interval the other is characterized by abrupt changes in the compositions of olivine fo28 to fo70 clinopyroxene mg 51 to 75 and plagioclase an24 to an51 over a 20 m vertical interval these suggest that the panzhihua intrusion opened at least twice for recharge of more primitive magmas strong depletion of incompatible trace elements such as zr in the cumulate sequence without corresponding enrichment in any border series is suggested to be evidence for significant loss of residual liquid at a late stage during solidification of the intrusion compared to other well studied layered intrusions the panzhihua intrusion contains fe ti oxides crystallized at a high temperature consistent with evidence obtained in earlier studies early appearance of liquidus fe ti oxides in the panzhihua magma is most likely a combined effect of a rather high degree of initial oxidation and elevated volatile fugacity

resolving shallow shear wave velocity structure beneath station cbn by waveform modeling of the mw 5 8 mineral virginia earthquake sequence abstract the 23 august 2011 m w 5 8 mineral virginia earthquake was the largest earthquake in the central and eastern united states in the past 100 years and it was well recorded by strong motion and broadband seismometers thus providing abundant ground motion data for earthquake ground motion studies the largest recorded ground motion among advanced national seismic system stations was at station cbn but the site effects at station cbn need to be understood because the strong motions recorded there do not represent bedrock site conditions on the radial component of these recordings the initial p wave is very weak and is followed by a strong signal 0 3 s later which is interpreted to be the s wave converted from the p wave ps at the interface between the sediments and bedrock we first estimate the subsurface shear wave velocity by modeling the ratio of the radial to vertical components of the initial p waves and then resolve the velocity structure and thickness of the unconsolidated sediments by modeling the ps wave the subsurface shear wave velocity is found to be approximately 300 m s consistent with field survey results the shear wave velocity at the bottom of the sediments is constrained to be in the range of 320 780 m s from which the thickness of the layer is estimated to be 100 230 m the estimates of shear wave velocity structure and thickness of the sediments are further improved by modeling the oscillatory waveforms between the p and s waves this study suggests that site characterization for the estimation of ground motion amplification at a site can be achieved inexpensively and noninvasively by modeling local p waveforms recorded at the site

genesis of middle miocene yellowstone hotspot related bonanza epithermal au ag deposits northern great basin usa epithermal deposits with bonanza au ag veins in the northern great basin ngb are spatially and temporally associated with middle miocene bimodal volcanism that was related to a mantle plume that has now migrated to the yellowstone national park area the au ag deposits formed between 16 5 and 14 ma but exhibit different mineralogical compositions the latter due to the nature of the country rocks hosting the deposits where host rocks were primarily of meta sedimentary or granitic origin adularia rich gold mineralization formed where glassy rhyolitic country rocks host veins colloidal silica textures and precious metal colloid aggregation textures resulted where basalts are the country rocks clay rich mineralization with silica minerals adularia and carbonate developed oxygen isotope data from quartz originally amorphous silica and gels from super high grade banded ores from the sleeper deposit show that ore forming solutions had 18o values up to 10 heavier than mid miocene meteoric water the geochemical signature of the ores including their se rich nature is interpreted here to reflect a mantle source for the epithermal suite elements au ag se te as sb hg and that signature is preserved to shallow crustal levels because of the similar volatility and aqueous geochemical behavior of the epithermal suite elements a mantle source for the gold in the deposits is further supported by the pb isotopic signature of the gold ores apparently the host rocks control the mineralization style and gangue mineralogy of ores however all deposits are considered to have derived precious metals and metalloids from mafic magmas related to the initial emergence of the yellowstone hotspot basalt derived volatiles and metal loid s are inferred to have been absorbed by meteoric water dominated geothermal systems heated by shallow rhyolitic magma chambers episodic discharge of volatiles and metal loid s from deep basaltic magmas mixed with heated meteoric water to create precious metal ore forming fluids colloidal nanoparticles of au ag alloy electrum naumannite ag2se silica and adularia likely nucleated at depth traveled upward and deposited where they grew large enough to aggregate along vein walls silica and gold colloids have been reported in hot springs from yellowstone national park suggesting that such processes may continue to some extent to the present however it is possible that the initial development of the mantle plume led to a major but short lived distillation process which led to the mid miocene bonanza ore forming event

groundwater dilution and residence times and constraints on chloride source in the mokai geothermal system new zealand from chemical stable isotope tritium and 36cl data the mokai geothermal system new zealand is located within a volcanic collapse structure comprised of flat lying silicic rocks the deep chloride fluid rises in the south inside the caldera margin near the surface the fluid flows laterally more than 12 km to the north because of the hydraulic gradient caused by 300 m of relief the maximum measured temperature of the production wells is near 323 c at 2500 m depth whereas temperatures in two wells on the northern margin of the upflow are 200 c with thermal inversions at 350 and 1000 m indicating lateral flow these two marginal wells have about 50 of the chloride of the deep fluid indicating dilution by cold ground water chloride bearing springs discharge 6 km north of the zone of upflow and are even further diluted by cold groundwater than the wells on the margin of the system the tritium data in this hydrologically rather simple system indicate that there is a mean residence time of greater than 100 years for the groundwater diluent also older water is mixed with 25 of young thermonuclear post 1955 water before the mixture dilutes outflowing chloride fluid from the deep system the deep chloride fluid has a 36cl cl ratio of 2 6 10 15 and a 36cl concentration of 106 atoms per 10 6 kg this fluid has a lower ratio by a factor of 90 and a higher absolute concentration by a factor of 7 than present day stream water however the marginal wells have been diluted by groundwater with at least 500 36cl atoms per 10 6 kg 30 times richer in 36cl than present day stream waters this spike is most likely due to circulation of precipitation formed during thermonuclear testing to depths of 1000 m though the component with the 36cl spike only makes a moderate 25 contribution to the groundwater diluent most of the diluent is much older pre 1955 the amount of 36cl in the deep fluid at mokai is 5 10 times less than that predicted from a calculation of the neutron fluxes in the silicic reservoir and underlying greywacke basement rocks this indicates that the chloride was not derived from host rock leaching in the upper 3 km rather the fluids have interacted with more primitive rocks below the drilled depths of the taupo volcanic zone with the chloride possibly derived from a magmatic brine

reflection and transmission imaging of the upper crust using local earthquake seismograms we utilize the characteristic features of primary p and sh wave coda and sp waveforms from local microearthquake data and perform prestacking 1d migration in an attempt to image prominent reflectors in the upper crust of the new madrid seismic zone nmsz this methodology applies to data from broadband stations parm and penm of the cooperative new madrid seismic network cnmsn nearby exploration well log acoustic data of the wilson 2 14 and dow chemical wilson number 1 wells are used to constrain the upper 4 km of p wave velocity model despite polarity differences among p sh and sp waveforms this technique demonstrates that consistent reflectors in the deep sedimentary section can be imaged commonly among the three wave types there are excellent correlations associated with the base of the upper cretaceous holocene mississippi embayment supergroup and the base of knox group which were also reported in a study of nearby seismic reflection profiles by hamilton and zoback 1982 the bonne terre formation seems to be a prominent seismic stratigraphic marker associated with an interface displayed in the profiling we find that earthquake event s p times must be 3 sec or more to resolve reflectors at about 4 km depth possible basement at about 4 0 to 4 5 km appears on the reflected p wave image for parm and sh wave image for penm we conclude that the velocity structure of the upper 4 km crust beneath parm can be represented by a constant velocity of graphic 1 and graphic 2 for the unconsolidated sediments and graphic 3 and graphic 4 for the paleozoic sedimentary rocks a constant velocity of graphic 5 and graphic 6 for the unconsolidated sediments and graphic 7 and graphic 8 for the paleozoic sedimentary rocks can represent structure beneath penm 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif 4 embed inline graphic 4 gif 5 embed inline graphic 5 gif 6 embed inline graphic 6 gif 7 embed inline graphic 7 gif 8 embed inline graphic 8 gif

an integrated study of crustal structure and regional wave propagation for southeastern missouri teleseismic receiver function analysis and published refraction studies are used to infer the existence of first order discontinuities within the crust and mantle of the ozark uplift at the incorporated research institutions in seismology iris station cathedral cave missouri ccm this information is then used to study the nature of regional wave propagation from the new madrid seismic zone to ccm across the ozark dome to interpret broadband seismograms written by small events receiver function inversion indicates a crust 40 km thick characterized by smooth velocity gradients down to the moho secondary ps conversions late in the receiver functions show the existence of a high velocity mantle layer 10 to 15 km thick at approximately 60 km depth with p wave velocity of about 8 5 km sec the data resolve both the top and bottom of the layer such high velocities suggest rocks with eclogite or dunite compositions regional data from the 26 september 1990 cape girardeau earthquake m 1 4 7 are used to model average crustal velocities and the nature of the velocity gradient near the moho through inversion of relative arrival times of observed phases regional p and s waveforms are exceptionally simple at ranges of 180 km showing the mantle head waves pn and sn with a triplicated pg and sg arriving within a few seconds respectively sp is quite prominent and is an accurate indicator of source depth for the cape girardeau event which occurred between 14 and 16 km depth there is no evidence for other major phases except rg after the sg arrival confirming the observation that the crust is dominated by smooth velocity gradients a grid search technique is used to model relative phase amplitudes to obtain the focal mechanism for the cape girardeau event allowable focal mechanisms are dominated by thrust faults striking ns or ne sw the inferred earth structure is used to model the 4 may 1991 risco event m 1 4 6 but observed differences in relative arrival times between p s and rayleigh phases suggest that crustal velocities are slightly lower within the mississippi embayment and that the uppermost mantle has a higher positive gradient than further northwest nevertheless sp constrains the source depth between 7 and 9 km and p sv and sh wave amplitudes yield mechanisms consistent with that obtained by the portable array for numerical data acquisition panda deployment waveforms from two small events with poor signal to noise ratios are compared with waveforms of the larger events to infer source depths modeling broadband waveforms from small local and regional events shows great promise in determining source parameters and inferring details of crustal and upper mantle structure however lateral heterogeneity in velocity structure will remain one of the principal obstacles to overcome

siderophile and chalcophile elemental constraints on the origin of the jinchuan ni cu pge sulfide deposit nw china abstract the jinchuan deposit nw china is one of the world s most important ni cu pge sulfide deposits related to a magma conduit system and is hosted in an ultramafic intrusion the intrusion is composed of lherzolite and dunite with the two largest sulfide ore bodies named as ore body 1 and 2 in its middle portion the sulfide ores may be disseminated net textured or massive the disseminated and net textured sulfide ores are characterized by variable but generally low pge concentrations 10 3200 ppb pt 240 9800 ppb pd 17 800 ppb ir 25 1500 ppb ru and 15 400 ppb rh in 100 sulfides the massive sulfide ores are extremely low in pt 4 to 4 5 10 5 the low pge contents suggest that the sulfide ores formed from the silicate magmas that had already experienced prior sulfide separation our calculations indicate that if the first stage basaltic magmas had contained 6 3 ppb pt 6 2 ppb pd and 0 1 ppb ir 0 008 sulfide removal would result in pge depletion in the residual magma with 0 57 ppb pt 0 25 ppb pd and 0 009 ppb ir the jinchuan sulfides were formed by a second stage of sulfide segregation from a pge depleted magma under silicate sulfide liquid ratios r factor ranging from 10 3 to 10 4 in a deep seated staging chamber the massive sulfide ores and some of the net textured sulfide ores exhibit strong negative pt anomalies that cannot be explained by sulfide segregation under variable r factors instead the sulfide melts that formed the massive ores were segregated from magmas experienced prior fractionation of pt fe alloy alternatively the pt may have been selectively leached by hydrothermal fluids during remobilization of the sulfide melts that produced the massive sulfides which occur in cross cutting veins we propose that the jinchuan intrusion and ore bodies were formed by injections of sulfide free and sulfide bearing olivine mushes from a deep seated staging chamber

in situ strontium and sulfur isotope investigation of the ni cu pge sulfide ore bearing kevitsa intrusion northern finland the 2 06 ga kevitsa mafic ultramafic intrusion in northern finland hosts a large disseminated ni cu pge deposit the deposit occurs in the ultramafic olivine pyroxene cumulates and shows a range in ni tenors varying from 4 7 wt regular ore to 10 wt ni pge ore there are also a metal poor sulfide mineralization false ore and contact mineralization that are uneconomic ni tenor 0 7045 in comparison to the estimated depleted mantle sr isotope ratio of 0 702 at 2 06 ga the sulfur 34s values are generally higher than 2 which together with the sr isotope data imply involvement of crustal material in the genesis of the kevitsa intrusion and its ores the 87sr 86sr i values obtained from the ore bearing domain of the intrusion show stratigraphic variation and exceed 0 7050 with the maximum value reaching up to 0 7109 in contrast in rocks around the ore domain the initial sr isotope compositions remain more or less constant 0 7047 0 7060 throughout the intrusive stratigraphy the isotope data suggest that the ore bearing domain of the intrusion represents a dynamic site with multiple injections of variably contaminated magma whereas the surrounding part of the intrusion experienced a less vigorous emplacement history no correlation is observed between the strontium and sulfur isotope compositions this is explained by bulk assimilation of the silicate magma in a deeper staging magma chamber and variable assimilation of sulfur during magma transport into the kevitsa magma chamber the low level of metals in false ore and the ni depleted nature of its olivine suggest that some sulfides may have precipitated and deposited in the feeder conduit during the initial stage of magma emplacement cannibalization of early formed sulfides by later magma injections may have been important in the formation of the economic ore deposit

bulk sediment qp and qs in the mississippi embayment central united states we have estimated p wave ands wave anelastic attenuation coefficients for the thick unconsolidated sediments of the mississippi embayment central united states using the spectral distance decay of explosion p and rayleigh waves the sediment trapped p wave psed is observed to ranges of 80 km at 10 hz and 1 hz rayleigh waves are observed out to 130 km from a 5000 lb borehole explosion in the northern part of the embayment rayleigh waves of 4 hz are seen to distances of 3 km from a smaller 50 lb explosion analysis of the group velocity and amplitude distance decay of both waves yields an average qs of 100 and qp of 200 for embay ment sediments that are independent of frequency scatter in the q estimates comes from interference of multiple p wave reverberations and rayleigh wave modes the attenuation model is self consistent in that it is the same as obtained by the analysis of synthetic seismograms using the inferred q values inferred qp and qs values are more than three times higher than previous estimates and imply that unconsolidated sediments of the embayment do not significantly attenuate small strain earthquake ground motions these estimates represent a lower bound to q of the sediments since significant scattering is observed in the waveform data that contributes to the distance decay of wave amplitude higher q values also imply that the unconsolidated sedi ments of the embayment will form an efficient wave guide for surface waves radiated from shallow earthquakes or large earthquakes that rupture into the sediments pro ducing high amplitude long duration wave trains that should be considered in earth quake hazard assessments

olivine and sulfur isotopic compositions of the uitkomst ni cu sulfide ore bearing complex south africa evidence for sulfur contamination and multiple magma emplacements the uitkomst complex in northern south africa is host to a ni cu deposit containing a minerable reserve of 2 9 mt massive ore with grades of 2 ni 1 cu and 6 ppm pt pd and an indicated plus inferred resource of 98 mt disseminated ore with grades of 0 6 ni 0 2 cu and 1 ppm pt pd based on similar age and composition to that of the bushveld complex the uitkomst complex is believed by some investigators to be a satellite body of the bushveld complex it has a tubular shape with an exposed surface area of about 0 8 8 km and a thickness of up to 1000 m apparently exploiting the bedding planes of gently dipping footwall sediments that include shale quartzite and dolomite the uikomst complex comprised of stratiform mafic and ultramafic rock units that from base to top include gabbro sulfide mineralized harzburgite unmineralized harzburgite pyroxenite gabbronorite and gabbro the compositions of olivine from different rock units are significantly different olivines from the gabbronorite unit are highly fractionated containing 30 mol fo forsterite mg2sio4 and 300 ppm ni olivines from the underlying pyroxenite and harzburgite units are much more primitive containing 86 91 mol fo abrupt changes in the contents of ni in olivine occur within the pyroxenite unit and between the mineralized and unmineralized harzburgite units the contents of ni in olivine from the unmineralized harzburgite unit are between 2900 and 3600 ppm the contents of ni in olivine from the underlying mineralized harzburgite units are 1500 ppm lower olivines from the lower part of the pyroxenite unit are similar to olivines from the underlying harzburgite unit whereas olivines from the upper part of the pyroxenite unit contain much lower ni 600 ppm numerical modelling suggests that the strikingly different compositions of olivine are related to different parental magmas with different mgo feo ratios and or ni contents the 34s values of the basal gabbro and unmineralized rock units range from 0 9 to 2 6 which are similar to typical mantle values 0 3 in contrast the 34s values of the sulfide ores in the harzburgite units are significantly lower varying between 2 6 and 7 1 the low 34s values of the sulfide ores indicate addition of 34s depleted crustal sulfur the obvious sources of such crustal sulfur are the malmani dolomite and the timebal hill shale that contain pyrite with negative 34s values up to 11 and 18 respectively sulfide saturation in the magma of the mineralized harzburgite units is thought to have resulted from addition of the crustal sulfur the resulting immiscible sulfide liquid droplets were then concentrated in the base of the magma channel some of the sulfide liquid was expelled into the basal gabbro that separated the active magma channel from the footwall quartzite new magma then entered the channel displacing most of the resident magma to form the unmineralized harzburgite the overlying pyroxenite gabbronorite and gabbro units formed either by in situ differentiation of the same magma giving rise to the underlying unmineralized harzburgite or by subsequent emplacement of a more evolved magma

mineralogic and stable isotope studies of hydrothermal alteration at the jinchuan ni cu deposit china the jinchuan intrusion hosts one of the largest magmatic ni cu sulfide deposits in the world net textured and disseminated pyrrhotite pentlandite and chalcopyrite are found in olivine rich rocks 60 80 vol that occur as a northwest southeast striking dike olivine in the intrusion has been variably converted to mixtures of serpentine and fine grained magnetite interstitial pyroxene and minor plagioclase have been altered to mixtures of chlorite amphibole epidote clinozoisite na rich feldspar and lesser amounts of calcite although the interstitial net texture of sulfide minerals surrounding olivine grains is preserved up to 30 vol percent of sulfide minerals are replaced by magnetite serpentine and chlorite an external origin for mg and si needed for the isovolumetric replacement of sulfides cannot be discounted but a local origin related to olivine and pyroxene alteration is favored serpentine and chlorite may be enriched in cu and ni but the enrichment can account for less than 1 percent of the metals lost during the replacement of sulfide minerals by silicates and oxides some of the metals and sulfur that were removed from the net textured sulfide assemblages have been redeposited on a centimeter scale in fine ribbons and veins within serpentine chlorite and amphibole sulfur isotope values of the pyrrhotite pentlandite chalcopyrite assemblage at jinchuan fall in the range of 2 to 8 per mil with over 80 percent of the values between 2 and 2 per mil immediate country rocks in the jinchuan area are precambrian granitoids schists and marbles with sulfur concentrations less than 100 ppm although the 34 s values of the main sulfide assemblage at jinchuan are in the range that is characteristic of mantle derived sulfur assimilation of sulfur from unexposed country rocks cannot yet be discounted secondary pyrite occurs in veins and stringers and rarely as a replacement of pyrrhotite and is characterized by 34 s values between 7 and 27 per mil the strongly negative 34 s values of secondary pyrite are thought to be a result of oxidation of primary magmatic sulfide assemblages and partial reduction of aqueous sulfate oxygen and hydrogen isotope values of silicate minerals suggest that at least two fluids have been involved in the hydrothermal alteration at jinchuan the 18 o values of plagioclase amphibole and serpentine all suggest the involvement of a fluid with a 18 o value between 2 and 5 per mil at 300 to 400 c the d values of amphibole and one population of serpentine suggest a d value for the fluid in the range of 45 to 63 per mil these values are consistent with the involvement of evolved seawater or a metamorphic fluid in the early stages of alteration the possible involvement of evolved seawater in hydrothermal alteration is consistent with a rift setting for the emplacement of the jinchuan intrusion however the wide range in serpentine d values computed d of the fluid 45 to 103 suggest either that serpentinization involved a mixture of evolved seawater and or metamorphic water and meteoric water or more likely that serpentine continued to exchange hydrogen isotopes with late stage meteoric waters after it formed

magma mixing recorded by sr isotopes of plagioclase from dacites of the quaternary tengchong volcanic field se tibetan plateau abstract the tengchong volcanic field east of the burma arc in sw china comprises numerous quaternary volcanoes the volcanic rocks can be grouped into four units numbered 1 4 from oldest to youngest units 1 3 and 4 are composed of trachybasalt basaltic trachyandesite and trachyandesite respectively whereas unit 2 consists of hornblende dacite primary minerals in the dacite include plagioclase clinopyroxene amphibole and magnetite all set in a glassy groundmass some of the dacites are moderately to highly weathered and show effects of low temperature alteration with loss on ignition loi up to 9 6 wt and positive correlations of loi with al2o3 but negative correlations with sio2 cao and na2o fresh dacites loi plagioclase in the fresh dacite has relatively high sr contents and 87sr 86sr ratios ranging from 0 7050 to 07125 except for one value of 0 7516 whereas plagioclase in the altered dacite has low sr contents and highly variable sr isotopic compositions 0 7039 0 7138 indistinguishable from those of the fresh rocks both an values and sr isotopic compositions of the plagioclase indicate mixing of mantle and crustally derived magmas we therefore propose that mantle derived basaltic magma caused partial melting of the lower middle crust and that mixing of the mafic and felsic magmas produced the dacite in staging magma chambers the dacites contain minerals crystallized from both the mafic and felsic magmas as well as a few xenocrysts plucked from the country rocks

seismic imaging of the site response using microearthquake recordings part ii application to the swabian jura southwest germany seismic network the subsurface site structure of the swabian jura southwest germany seismic network has been modeled from the inversion of locally recorded sh wave microearthquake seismograms the observed records have been deconvolved from the effects of apparent source pulse broadening due to the combined influence of frequency bandlimited source signals absorption peg leg multiple reflections and the recording system following the procedure of scherbaum and stoll 1985 corresponding pseudo reflection seismograms were calculated based on the kunetz claerbout relation for sh waves and inverted using a levison recursion algorithm the final structural models have been optimized in terms of numbers of layers and depth resolution using ferber s 1985 noise stabilization technique the resulting impedance models for the swabian jura southwest germany seismic network show some strongly correlated reflectors in the uppermost layers which are well understood in terms of the local stratigraphy the comparison of the inverted impedance model hsn with the p wave velocity log from a nearby exploration drilling trochtelfingen beb shows a high degree of similarity of the dominating reflectors down to a depth of several hundred meters as a consequence the coda generating process for the early part of the coda of the observed swabian jura microearthquake seismograms wood anderson magnitude mwa 3 0 can be completely interpreted as an effect of the local subsurface structure

the evolution of the waiotapu geothermal system new zealand based on the chemical and isotopic composition of its fluids minerals and rocks abstract the waiotapu geothermal system is hosted by silicic rocks of the taupo volcanic zone new zealand exploration drilling in the late 1950s down to 1100 m provided physical information on the system measured temperatures show a boiling profile to 295 c with shallow inversions particularly in the north total discharge fluid samples were collected the geothermometry and measured temperatures show that fluids derive mainly from a shallow 400 m deep reservoir at about 225 c petrologic study of drillcore samples recovered from seven wells reveals an alteration assemblage of quartz and albite adularia with a variable distribution of chlorite pyrite calcite zeolites epidote pyrrhotite sphene leucoxene apatite and minor base metal sulfides white mica is a late overprint particularly well developed at shallow depths surficial alteration of kaolin cristobalite alunite and smectite clays reflect alteration by acid sulfate steam heated waters the activities of components in minerals determined from microprobe analyses and composition activity relations and fluids speciated to reservoir conditions indicate equilibrium now exists between the fluids and white mica the na k ratio of the fluid is being controlled by dissolution of albite and adularia while its h 2 h 2 s ratio is buffered by pyrite replacing pyrrhotite the fluids are now slightly undersaturated with respect to calcite the present deep fluids boil adiabatically from at least 300 c to 230 c at depths of 500 m this ascending chloride fluid is variably diluted by a steam heated water of zero chloride that lies over and occurs on the margin of the system like a discontinuous umbrella the steam heated water is relatively co2 rich 0 1 m the cooling at shallow levels by this mixing has shifted the alteration from albite adularia stability to white mica stability this shift is enhanced by the co2 rich nature of the diluent dilution of ascending chloride fluids by shallow waters is also supported by the oxygen and hydrogen isotopic composition of the mixture with the deep fluid being enriched in 18o and d from local meteoric by 7 and 10 respectively the patterns in whole rock 18o indicate that they were largely shifted in isotopic composition prior to incursion of steam heated waters possibly induced by a series of hydrothermal eruptions 900 years ago in contrast the 18o composition of late vug calcite indicates its formation is related to the initial incursion of steam heated groundwater and subsequent cooling this is supported by fluid inclusion evidence the d shift from local groundwater composition and the 13c composition of co2 determined from calcite 4 to 6 may be evidence for a magmatic input to the meteoric convection cell the shallow portion of the waiotapu geothermal system has recently evolved both chemically and physically by incursion of fluids from a steam heated carapace continued refluxing of these relatively cool hybrid fluids progressively deeper with their recycled co2 content will hasten hydrolytic leaching in contrast to a single pass of adiabatically cooling deep fluids this action accompanied by argillic alteration may eventually seal the deeper portions of the system hastening its demise there is evidence for similar events occurring in the fossil environment at epithermal depths

boiling and dilution in the shallow portion of the waiotapu geothermal system new zealand abstract the waiotapu geothermal system is the largest in terms of surface extent and heat flow 17 km2 and 600 mw respectively of the 20 major geothermal systems in the taupo volcanic zone new zealand two extinct dacite cones and a rhyolite dome rise about 500 m above the waiotapu valley the majority of thermal features occurs in the valley over a relief of only 100 m and lies within coincident apparent resistivity and 30 m depth thermal anomalies thermal features comprise near neutral ph chloride springs often boiling acid sulfate springs and mud pools and mixed waters the latter including both bicarbonate chloride and acid sulfate chloride springs the majority of the sulfate discharges to the surface in the northern higher altitude area while most chloride that reaches the surface does so in the southern portion of the system comparison of measured and calculated surface chloride flux the latter from measured heat flow and reservoir chloride concentrations indicates that at least half of the deep chloride does not discharge at the surface but flows laterally to the south at shallow depths mixing with groundwater the composition of well discharges indicates a shallow 400 m reservoir of chloride fluid about 1350 mg cl kg at 230 c is diluted by a co2 rich steam heated water nil chloride at about 160 c the latter located on the margins of the system this same dilution trend is apparent from the compositional variation and k na and k mg geothermometry of hot spring waters however there is chemical and stable isotope evidence from hot springs that cold groundwater also acts as a diluent at shallow levels and very near the surface steam heated acid sulfate waters mix with the upflow boiling of the deep chloride fluids prior to dilution results in the stabilization of k feldspar in contrast dilution at shallower depths by the steam heated waters both co2 rich and acid sulfate leads to the water compositions initially shifting to k mica and interstratified clay stability and to kaolinite stability with further dilution and temperature decrease the composition and distribution of these fluids are consistent with alteration mineralogy and zonation observed in drill core although boiling occurs at deeper levels and up to the surface in the upflow zone at waiotapu mixing is also common and is the dominant process on the margin and in the near surface portion of the system boiling of deep chloride fluid is very common in the upper 1 2 km of the upflow zone of most geothermal systems though it may be quenched by mixing with marginal waters either cold groundwater in high relief terrane or steam heated waters in areas of lower relief co2 rich steam heated waters are common on the margins of systems and will generally underlie the near surface acid sulfate steam heated waters interaction with co2 rich waters will form k mica and interstratified clays while acid sulfate waters cause kaolinite and even alunite to form the former assemblage is commonly associated with typical low sulfidation epithermal gold mineralization as wallrock alteration where gold bearing veins comprise adularia and illite in contrast kaolinite is rare and alunite absent from a direct spatial and genetic association with gold mineralization in this environment this implies that mixing of the deep neutral ph chloride fluid with surficial acid sulfate waters does not commonly lead to ore grade gold deposition mixing with and cooling by co2 rich steam heated waters leads to clay stability accounting for the large halos of clay alteration and low grade metal anomalies which often surround veins of high gold grade in contrast mixing with surficial acid sulfate waters is unlikely to cause precious metal mineralization because the chloride fluids have already lost the majority of their gold through deeper boiling and dilution

upper mississippi embayment shallow seismic velocities measured in situ abstract vertical seismic compressional and shear wave p and s wave profiles were collected from three shallow boreholes in sediment of the upper mississippi embayment the site of the 60 m hole at shelby forest tennessee is on bluffs forming the eastern edge of the mississippi alluvial plain the bluffs are composed of pleistocene loess pliocene pleistocene alluvial clay and sand deposits and tertiary deltaic marine sediment the 36 m hole at marked tree arkansas and the 27 m hole at risco missouri are in holocene mississippi river floodplain sand silt and gravel deposits at each site impulsive p and s waves were generated by man made sources at the surface while a three component geophone was locked downhole at 0 91 m intervals consistent with their very similar geology the two floodplain locations have nearly identical s wave velocity vs profiles the lowest vs values are about 130 m s 1 and the highest values are about 300 m s 1 at these sites the shear wave velocity profile at shelby forest is very similar within the pleistocene loess 12 m thick in deeper older material vs exceeds 400 m s 1 at marked tree and at risco the compressional wave velocity vp values above the water table are as low as about 230 m s 1 and rise to about 1 9 km s 1 below the water table at shelby forest vp values in the unsaturated loess are as low as 302 m s 1 vp values below the water table are about 1 8 km s 1 for the two floodplain sites the vp vs ratio increases rapidly across the water table depth for the shelby forest site the largest increase in the vp vs ratio occurs at 20 m depth the boundary between the pliocene pleistocene clay and sand deposits and the eocene shallow marine clay and silt deposits until recently seismic velocity data for the embayment basin came from eartquake studies crustal scale seismic refraction and reflection profiles sonic logs and from analysis of dispersed earthquake surface waves since 1991 seismic data for shallow sediment obtained from reflection refraction crosshole and downhole techniques have been obtained for sites at the northern end of the embayment basin the present borehole data however are measured from sites representative of large areas in the mississippi embayment therefore they fill a gap in information needed for modeling the response of the embayment to destructive seismic shaking

reevaluation of the role of external sulfur addition in the genesis of ni cu pge deposits evidence from the nebo babel ni cu pge deposit west musgrave western australia the nebo babel ni cu pge sulfide deposit located in the west musgrave block western australia is hosted within a tube like concentrically zoned gabbronorite magma conduit emplaced at 1068 ma the nebo babel deposit is associated with the ca 1078 ma giles complex which is part of the warakurna large igneous province previous geologic and geochemical studies have shown that the nebo babel consists of chemically related but temporally distinct magma pulses the initial magma pulses which were the most primitive and the most contaminated formed the marginal units of the conduit the later pulses were emplaced into the core of the conduit the chilled margin rocks contain sulfide globules mineralization is confined to the early magma pulses and consists of massive sulfide breccias and stringers and disseminated gabbronorite hosted sulfides the ni tenor of the massive sulfides which have undergone sulfide liquid fractionation and the disseminated sulfides are almost the same indicating that both formed at similar r factors the whole rock massive and disseminated sulfides contain 650 ppb and 60 to 500 ppb total pge respectively all of the nebo babel rock units are slightly pge depleted with cu pd ratios higher than primitive mantle indicating early saturation and segregation of a sulfide and or pgm rocks with trace cumulus sulfides have the lowest cu zr and highest cu pd ratios and the most fractionated metal patterns indicating that these units have undergone the highest degrees of ni cu and pge depletion the average 34s value of all nebo babel disseminated and massive sulfides is 0 4 0 2 per mil which is consistent with the s originating in the mantle sulfur saturation did not occur in situ and is inferred to have been triggered by assimilation of felsic orthogneiss perhaps in the parental magma chamber this initial magma pulse with entrained sulfides formed marginal units of the nebo babel intrusion some of the entrained sulfides accumulated within physical traps on the way into the conduit and or at the exit from the chamber these sulfides were later emplaced along the footwall contact as massive and or marginal fragment laden sulfide liquid distribution of the disseminated sulfides was influenced by the conduit geometry and magma flow dynamics the final and volumetrically dominant barren magma pulse underwent crystal fractionation and oxide precipitation in the core of the nebo babel intrusion which in turn caused sulfide saturation and formed trace but pge depleted sulfides in these units the nebo babel deposit has a number of features in common with other ni cu pge deposits hosted in dynamic magma conduits e g voisey s bay such as multiple magma pulses and sulfide entrainment from depth rather than in situ sulfide segregation however si addition was the primary cause of sulfide saturation and external s addition did not play a role in the genesis of the nebo babel deposit

the source of halogens in geothermal fluids from the taupo volcanic zone north island new zealand abstract forty seven samples of deep geothermal well fluids and hot springs from 14 geothermal sites in the taupo volcanic zone tvz north island new zealand were analyzed for cl br and li concentrations and 37cl 7li 18o and d values the main purpose of this study was to identify the sources of salinity in the tvz fluids and to assess the processes that control stable chlorine isotopic fractionation in the geothermal waters the samples were obtained from deep wells in the mokai ohaaki wairakei rotokawa kawerau ngatamariki and tauhara geothermal fields and from the hot springs at rotorua waiotapu lake taupo waimangu waikite orakei korako and tokaanu two main meteoric recharge areas were identified in the central tvz one located to the ne with 18o and d values of 5 5 and 35 respectively and the other to the sw with a 18o value of 6 7 and d value of 43 water rock interactions in most of the geothermal fluids resulted in a 18o shift to more positive values up to 1 for mokai and over 3 for kawerau the 7li values range from 2 9 to 2 0 and suggest that the deep geothermal fluids have interacted with rocks with low 7li values the highest 7li values 1 4 in the reservoir fluids were found at kawerau where the low quartz content of the greywacke may result in the depletion of 6li the 37cl values of the samples ranged from 1 0 to 0 8 the 37cl values of 0 2 0 1 and 0 0 were measured in samples from orakei korako waiotapu and waimangu respectively and these are interpreted to have been affected by surface evaporation and distillation processes excluding these data most waters with high cl br ratios had positive 37cl values the cl br molar ratios in well samples ranged from 659 to 1664 and the 37cl values from 1 0 to 0 8 the hot springs had cl br molar ratios ranging from 858 to 1611and 37cl values from 0 8 to 0 7 overall the cl br molar ratios of the fluids are comparable with published data on basaltic magmas and these magmas are inferred to be the main source of halogens in the geothermal fluids however the geothermal fluids can be separated into two main groups one associated with rhyolitic magmas characterized by positive 37cl values and high cl br molar ratios and other related to andesitic magmas with negative 37cl values and lower cl br molar ratios we suggest therefore that the isotopic fractionation of the stable cl isotopes is related to the difference in water contents of andesitic and rhyolitic magmas and that the fluid phase is enriched in 37cl during magmatic evolution there is no evidence of isotopic fractionation during the transit of the geothermal fluids from the reservoir to the surface but evaporation and distillation processes at the surface can affect the 37cl values

the isotopic and chemical composition of co2 rich thermal waters in the mont dore region massif central france chemical and isotope compositions of fluid samples collected between 1974 and 1986 from 52 springs or shallow boreholes located in the mont dore region massif central france were examined some springs and wells were sampled several times during this period the fluids emerge from quaternary volcanic rocks or paleozoic granite at temperatures between 4 and 62 c and the origin of the h2o is meteoric the waters can be classified into three groups bicarbonate fluids mixed bicarbonate chloride fluids with a mineralization up to 8 g l and acid sulfate fluids only two fluids contain sufficient cl to be considered as mature waters previous work has demonstrated that they all contain partly mantle derived co2 gas and that the co2 rich gas phase and bicarbonate chloride waters are separated at substantial depth mineralized fluids circulate at depth and undergo several processes such as cooling or dilution with recent freshwater during their ascent to the surface therefore the co2 rich gas phase can be partly dissolved in the freshwater or in deep fluids after their dilution this process leads to the dissolution of surrounding rocks such dissolution is discussed on the basis of major element concentrations na k ca mg as well as the sr 87 86 isotope ratio dissolution of s bearing minerals has also been demonstrated the presence of the co2 rich gas phase also leads to isotope exchange between co2 and h2o some mineralized fluids are less affected by these processes than others in which case they display the chemical and isotopic characteristics of the original deep fluids it was shown that the applicability of geothermometer calculations for these waters is hampered by several processes that modify the chemical composition however some geothermometers can be used for estimating the temperature of the deep fluids using the chemical composition of the less modified fluids they indicate that fluids emerging from volcanic rocks in the dordogne valley reach temperatures of around 100 130 c at depth while the temperature of the fluid that issues from the granite at saint nectaire is 160 175 c at depth

intrusive and basement rock sources of lead in hydrothermal systems of the taupo volcanic zone new zealand abstract the taupo volcanic zone is a complex volcanic tectonic region over 250 km long corresponding to the volcanic arc of the taupo hikurangi subduction system volcanism is dominantly rhyolitic with minor amounts of andesite dacite and basalt the volcanics overlie a downfaulted basement of mesozoic metasediment waipapa and torlesse terranes over twenty major geothermal systems are active related to the young volcanism samples of sulfides galena sphalerite chalcopyrite and pyrite from five of the geothermal systems were collected from drill core and their pb isotopic compositions measured representative fresh samples from all volcanic and basement rock types of the region were also analyzed and show a range of values by which they may be distinguished sulfides from the broadlands and waiotapu geothermal systems are homogeneous in their pb isotopic compositions with values similar to the average for the fresh rhyolites and andesites the results indicate that the source of pb and possibly other metals in the broadlands and waiotapu hydrothermal fluids is related to the parent magma of the volcanics a magmatic fluid could be the source consistent with independent geochemical and isotopic evidence for other magmatic fluid derived components at broadlands and to a lesser extent at waiotapu which are both anomalously mineralized in precious and base metals in contrast pyrite pb from the unmineralized kawerau geothermal system has isotopic compositions which vary over a range similar to that of the underlying waipapa metasedimentary basement present at depths of only 1000 m this observation suggests that the pb at kawerau was mainly leached from the basement rocks with a component of isotopically homogenous magma related pb not present in the hydrothermal fluids isotopic compositions of pb from the unmineralized wairakei and mokai systems are intermediate between the broadlands and kawerau examples these data are interpreted to result from leaching of pb from both the basement and volcanic rocks consistent with the thick at least 3 km sequence of volcanics in the center of the zone where wairakei and mokai are located these results suggest that epithermal gold prospects may be distinguished on the basis of their pbisotopic signature those exhibiting a homogeneous and magmatic signature have a higher potential to contain ore all else being equal because of the potential for higher magmatic derived metal concentrations in the hydrothermal fluid this suggestion appears to be applicable only to dilute hydrothermal systems perhaps because the low salinity precludes leaching as an effective process to solubilize metals

nehrp soil classifications for estimating site dependent seismic coefficients in the upper mississippi embayment abstract local soil conditions have a profound influence on the characteristics of ground shaking during an earthquake exceptionally deep soil deposits on the order of 100 1000 m deep are found in the upper mississippi embayment of the central united states shear waves sh from earthquakes in the new madrid seismic zone are expected to be strongly affected by the sharp impedance contrasts at the bedrock sediment interface attenuation of seismic waves in the soil column and the sh wave velocities of the more poorly consolidated near surface 50 m soils sh wave velocities of the near surface soils at nearly 400 sites in the upper mississippi embayment were determined using conventional seismic sh wave refraction and reflection techniques based on the average sh wave velocities of the upper 30 m of the soils sites in the mississippi river floodplain portion of the study area are predominantly classified as site class d 180 360 m s in accordance with the 1997 nehrp provisions sites away from the active floodplains in western kentucky and western tennessee the sh wave velocities of the upper 30 m of soils typically ranged from mid 200 to mid 300 m s several sites in western kentucky had averaged sh wave velocities greater than 360 m s thereby qualifying them as site class c 360 760 m s in accordance with the 1997 nehrp provisions one dimensional site effects including amplification and dynamic site period were calculated for a representative suite of sites across the upper mississippi embayment at latitude 38 5 although seismic attenuation is greater in the mississippi river floodplain i e thicker lower velocity material the site effects tend to be greater than in the uplands of western tennessee because of larger impedance contrasts within the near surface soils

shear wave velocity of the sedimentary basin in the upper mississippi embayment using s to p converted waves from mid october 1989 to august 1992 40 three component panda portable array for numerical data acquisition stations were deployed in the central new madrid seismic zone three component digital seismograms recorded by the panda stations in the region are characterized by 1 the very weak direct s arrivals on the vertical component which can be identified unambiguously from the two horizontal components and 2 at least two prominent secondary arrivals between the direct p and s arrivals one sp dominant on the vertical component and another ps with smaller amplitude on the two horizontal components travel time differences between the sp and s and between the p and ps are the same for different earthquakes recorded at the same station but are different at different stations even for the same event polarization analyses of three component seismograms and travel time measurements confirm the interpretation that these two secondary arrivals are the p to s ps and s to p sp converted waves that occur at the bottom of the sedimentary basin beneath each station since abundant well log data are available in the upper mississippi embayment the thickness of the sediments beneath each seismic station can be estimated travel time differences between the direct and the converted waves can be used to calculate average shear wave velocity for the sediments beneath each station the estimated shear wave velocities of the sediments beneath panda stations vary from 0 45 to 0 67 km sec the higher shear wave velocity associated with thicker sediments can be interpreted as a consequence of increasing compaction of unconsolidated sediments due to increasing overburden

the structure of the mokai geothermal field based on geophysical observations abstract the mokai geothermal area about 25 km northwest of taupo has only minor thermal manifestations with a natural heat output of about 6 mw in late 1976 a roving dipole resistivity survey was made in the area surrounding mokai springs since then an extensive schlumberger resistivity survey has been made using two spacings nominally 600 m and 1200 m covering an area of about 4 b v n 2 around the mokai area interpretation of all the resistivity data suggests the area of mokai geothermal field below which high temperatures may be expected at depth is about 12 16 km 2 low resistivities from soundings within this area indicate highly conductive saline geothermal fluids at a depth of about 60 m although below this the resistivity increases suggesting a lowering of porosity the interpretation of resistivity measurements suggests a considerable subterranean flow of geothermal fluids northward from the mokai geothermal field and a further 76 mw of heat is estimated to be carried by springs and seeps into the deeply incised waipapa stream a second low resistivity region occurs at the waikato river about 12 km north of the geothermal field with an area of 3 4 km 2 there are indications that this anomaly is caused by hot geothermal fluids and it is suggested here that these geothermal fluids have their origin at the mokai geothermal field on this basis an estimate of the total heat output of the mokai geothermal area is 400 160 mw temperature in a drill hole within the geothermal field as outlined by this study reach a maximum of 290 c

multiple late holocene earthquakes along the reelfoot fault central new madrid seismic zone the reelfoot fault is an east vergent reverse fault underlying the lake county uplift a low amplitude late holocene anticline bordered on the east by the 32 km long reelfoot scarp fluvial deposits across the scarp define an 8 m high east facing monocline most near surface deformation along the scarp is accommodated via folding rather than faulting we interpret the scarp as a fault propagation fold developed over a wcst dipping reverse fault interpreted from shallow seismic reflection data trench exposurcs provide evidence for three episodes of deformation along the reelfoot fault within thc past approximately 2400 years between a d 780 and 1000 between a d 1260 and 1650 and during a d 1812 our best estimate of the average recurrence interval for deformation along the scarp is 400 500 years each episode of deformation had a slightly different style the third most recent event produced a small graben a few tens of centimeters deep in the hanging wall of the reverse fault the second most recent earthquake produced about 1 3 m of throw in the graben as well as folding along the updip projection of the reverse fault and development of the scarp thesc relations suggest that graben development increased through time concomitant with growth of the monocline or that the events are of different magnitude the 1811 1812 episode of deformation produced abundant liquefaction prominent folding of fluvial strata along the scarp and minor faulting in the graben

sr and pb isotopic disequilibrium between coexisting plagioclase and orthopyroxene in the bushveld complex south africa microdrilling and progressive leaching evidence for sub liquidus contamination within a crystal mush progressive leaching of plagioclase for sr iso topes and microdrilling for sr and pb isotopes from grains of plagioclase and orthopyroxene from the critical zone and the lower zone indicates that these minerals are not in isotopic equilibrium leaching suggests critical zone plagioclase either lost rb or had a more radiogenic sri rim relative to the core whereas plagioclase from an upper zone sample is isotopically homogeneous for sri microdrilling analyses of plagioclase from the lower and critical zones consistently have a higher initial 87 sr 86 sr sri and a less radiogenic modeled 238 u 204 pb composition l2 than coexisting ortho pyroxene the range of calculated sri for plagioclase and orthopyroxene is 0 70506 0 70662 34 and 0 70290 0 70654 36 respectively the average difference in sri between mineral pairs was 0 00095 the range of calculated l2 for plagioclase and orthopyroxene is 9 42 10 30 average 9 7 and 9 83 15 75 average 10 1 respectively the range of measured 208 pb 206 pb for plagioclase and orthopyroxene is 34 757 36 439 33 and 36 669 41 845 85 respectively one orthopyroxenite without evidence for more than one population of crystal size distribution nonetheless had sri 0 70654 36 with calculated l2 of 10 32 for larger grains as compared with sri 0 70290 32 and calculated l2 of 9 97 for smaller grain size fractions isotopic results from this study demonstrate that whole rock isotopic data may not provide the appropriate level of detail necessary to address some processes in the bushveld complex however systematic changes have the potential to elucidate the timing of contamination with regard to other processes crystal aging compaction driven recrystallization and mineral exsolution occurring within a slowly cooled crystal liquid vapor mush system

open magma chamber processes in the formation of the permian baima mafic ultramafic layered intrusion sw china abstract the baima mafic ultramafic layered intrusion of the 260 ma emeishan large igneous province elip hosts the second largest fe ti v oxide deposit in the panxi region sw china it is a 1600 m thick layered body intruded by slightly younger syenitic and granitic plutons the intrusion includes the lower and upper zones troctolite and olivine pyroxenite of the lower zone contains conformable oxide ore layers whereas the upper zone consists of olivine gabbro and gabbro with abundant apatite in the higher level the crystallization order of the silicates in the baima intrusion is olivine plagioclase clinopyroxene fe ti oxides titanomagnetite and ilmenite crystallized after olivine and possibly plagioclase the oxide ores in the lower zone show slightly lree enriched patterns with la yb n values between 2 0 and 6 4 and positive eu anomalies eu eu of 1 0 to 2 7 in contrast olivine gabbros in the lower zone display stronger lree enrichments la ybn 7 7 14 0 and positive eu anomalies eu eu 2 8 3 3 gabbros in the upper zone have ree profiles characterized by intermediate lree enrichments with la yb n values of 3 2 to 11 2 and positive eu anomalies of 2 1 to 3 0 primitive mantle normalized trace element patterns are characterized by negative la ce th sm and positive nb ta ba and ti anomalies in oxide ores and negative th u zr hf and positive ba sr and ti anomalies in olivine gabbro and gabbro fo of olivine and an of plagioclase remain roughly constant from 0 to 90 m in the lower zone indicating that the magma chamber was continuously filled by compositionally similar magmas during the initial stage three magma replenishments occurred afterwards in the upper part of the lower zone and the upper zone based on compositional reversals of plagioclase olivine and sr isotope mass balance calculations show that the baima parental magma can produce all oxide ores under closed system conditions a wide range of an values of plagioclase within thin sections and disequilibrium sr isotopic compositions of plagioclase both along the stratigraphic profile 87sr 86sri 0 70312 0 70510 and within thin sections indicate convection and co accumulation of cumulus plagioclase that had crystallized from different magmas we propose that the 1600m thick baima intrusion formed in an open and isotopically heterogeneous magma chamber that was periodically recharged by compositionally similar or more primitive magmas in each replenishment cycle the magma underwent progressive crustal contamination and fractional crystallization convection and sorting of crystals based on density differences result in igneous layering characterized by intervals of oxide ores troctolite and olivine gabbro

aquia aquifer dissolved cl and 36cl cl implications for flow velocities the aquia aquifer southern maryland contains a remarkably smooth cl profile 0 46 3 23 ppm along its flow path this is interpreted as a record of historic changes in the deposition of cl in this region those changes have been influenced by the rise and fall of sea level which has altered the distance of the recharge region from the coastline by 200 km the 36cl concentration along the flow path is not as smooth as the cl profile historic variations in cosmogenic production atmospheric transport precipitation and evapotranspiration all might have influenced 36cl concentrations a general similarity between the 36cl and cl profiles suggests that changes in precipitation and evapotranspiration rates which influence both tracers similarly are particularly important to reconcile 14c 36cl and hydrologic data we propose a two tier model for flow in the aquia shallower portions of the aquifer 60 m were subjected to hydraulic gradients and flow rates approximately 5 times larger during the pleistocene than modern prepumping rates at greater depths flow rates were much slower and less variable water in this region may be old enough to record some 36cl decay

the paleoproterozoic komatiite hosted pge mineralization at lomalampi central lapland greenstone belt northern finland several komatiite hosted ni cu pge deposits occur in archean and paleoproterozoic greenstone belts in finland some of these deposits are enriched in platinum group elements especially in pd and pt the lomalampi pge cu ni deposit is associated with a peridotitic cumulate body of the sattasvaara formation in the paleoproterozoic central lapland greenstone belt the sulfides in the deposit occur in disseminated form whole rock sulfur contents are 0 4 2 wt and ni contents are 0 5 wt and cu 0 4 wt while pge contents exceed 500 ppb the sulfides consist of magmatic pentlandite pyrrhotite and chalcopyrite and have not been substantially modified by metamorphic processes palladium minerals are associated with sulfides and silicates but the only pt bearing phase sperrylite occurs mainly within silicates the host rock of the deposit is a chromite undersaturated al undepleted high mg basalt or low mg komatiite in contrast to most other komatiite hosted ni cu pge deposits world wide that have pt pd around 0 5 the lomalampi deposit is enriched in pt over pd pt pd 2 only a weak contamination signal in the host cumulate is evident in ree data but a strong signal is evident in s isotope ratios 34s 10 to 15 which differ substantially from the mantle value 0 2 geochemical characteristics e g pge enrichment and r factor modeling indicate certain similarities between lomalampi and the raglan ni cu pge deposits of canada the combined data suggest that lomalampi formed through contamination of a pge rich magnesian magma with s rich country rocks this suggests that the extensive central lapland greenstone belt is favorable for komatiite hosted ni cu pge deposits which are substantially enriched in platinum and palladium

explosion source strong ground motions in the mississippi embayment two strong motion arrays were deployed for the october 2002 embay ment seismic excitation experiment to study the spatial variation of strong ground motions in the deep unconsolidated sediments of the mississippi embayment because there are no comparable strong motion data from natural earthquakes in the area each linear array consisted of eight three component k2 accelerographs spaced 15 m apart situated 1 2 and 2 5 km from 2268 kg and 1134 kg borehole explosion sources respectively the array data show distinct body wave and surface wave arrivals that propagate within the thick unconsolidated sedimentary column the high velocity basement rocks and small scale structure near the surface time domain coherence of body wave and surface wave arrivals is computed for acceleration velocity and displacement time windows coherence is high for relatively low frequency vertical component rayleigh waves and high frequency p waves propagating across the ar ray prominent high frequency ps conversions seen on radial components a proxy for the direct s wave from earthquake sources lose coherence quickly over the 105 m length of the array transverse component signals are least coherent for any ground motion and appear to be highly scattered horizontal phase velocity is com puted by using the ratio of particle velocity to estimates of the strain based on a plane wave propagation model the resulting time dependent phase velocity map is a useful way to infer the propagation mechanisms of individual seismic phases and time windows of three component waveforms displacement gradient analysis is a complementary technique for processing general spatial array data to obtain hori zontal slowness information

129i and 36cl concentrations in waters of the eastern clear lake area california residence times and source ages of hydrothermal fluids abstract the clear lake area of northern california is the location of hot spring activity some of which is associated with the formation of au and hg deposits we measured 129 i i and 36 cl cl ratios in nine warm springs formation springs six cold springs with elevated levels of cl and i mineral springs and five springs of recent meteoric origin dating of the i in the formation waters indicated that sources of i in these waters are formations with minimum ages between 60 and 80 ma this age range is in good agreement with the ages of the franciscan complex and the great valley sequence the dominant formations in this area because the mineral waters are essentially formation waters diluted with meteoric water i in these waters is of the same origin residence times of the waters were calculated based on the build up of129i and 36cl as a consequence of the presence of u and th in the crust the residence time of the formation waters in the great valley sequence the location for most of these springs was probably not longer than 84 000 yr the concentrations found for 36cl and 129i in the mineral waters indicate that these waters have residence times of similar magnitude in formations such as the franciscan complex or the clear lake volcanics which have slightly higher levels of u and th than the great valley sequence