electric and kinematic structure of the oklahoma mesoscale convective system of 7 june 1989 abstract balloon soundings of electric field in oklahoma mesoscale convective systems mcs s were made by the national severe storms laboratory nssl during the spring of 1989 a sounding made in the rearward edge of an mcs stratiform rain area on 7 june 1989 is the centerpiece of this study we used data from doppler radars a lightning ground strike location system satellite and other sources to relate the mesoscale attributes of the mcs to the observed electric field profile the stratiform area did not lag an organized convective line but was apparently initiated by anvil precipitation downwind of convective cells that were at the west and southwest flanks of the mcs the mature system produced a bipolar cloud to ground lightning pattern in which most flashes of positive polarity came to ground in the downshear anvil or stratiform region the bipole was oriented from 220 parrallel to upper level geostrophic flow and its length was 190 km we visually observed lightning flashes in the stratifo

the effect of crystal melt partitioning on the budgets of cu au and ag we have performed five separate sets of experiments to elucidate the effects of magnetite ulvospinel magnetite solid solution and pyrrhotite crystallization on the budgets of au cu and ag at magmatic conditions the experiments were done in both hydrous and anhydrous assemblages at temperatures between 800 and 1050 c pressures from ambient to 140 mpa log f o2 from nno 0 25 to nno and log f s2 from 1 5 to 3 0 nernst type partition coefficients 1 at 800 c in a water saturated assemblage are d agmt melt 2 10 4 2 10 9 d cumt melt 0 82 0 69 d cuusp melt 26 17 d auusp melt 50 31 d cupo melt 174 25 nernst type partition coefficients 1 at 1050 c in an anhydrous assemblage are d cupo melt 200 d agpo melt 58 8 d aupo melt 120 50 the calculated values for d auusp melt and d cuusp melt indicate that the addition of ti to magnetite increases significantly the au and cu scavenging potential of ulvospinel relative to end member magnetite partition coefficients for cu and au between pyrrhotite and melt indicate that a temperature change from 1050 to 800 c in an anhydrous and hydrous assemblage respectively results in no observable change in cu partitioning the calculated partition coefficients are used to model the effect of crystal fractionation on the concentrations of ag cu and au model results suggest that the co crystallization of magnetite and pyrrhotite sequester no more than 2 ag 7 cu and 37 au from the melt over the first 25 solidification if the melt reaches volatile saturation after 25 crystallization the presence of end member magnetite and pyrrhotite do not appear to inhibit the cu au and ag ore potential of the magma ulvospinel magnetite however may reduce the au concentration in the melt by approximately one third relative to its initial value that decreases the overall au available to partition into the volatile phase

cloud to ground lightning throughout the lifetime of a severe storm system in oklahoma cloud to ground cg lightning data are examined relative to digitized radar data for a storm system that occurred in oklahoma on 26 may 1985 this system evolved through three stages 1 two lines of cells one near the dryline and the other 60 km ahead of it 2 a supercell storm and 3 a mesoscale convective system mcs the behavior of lightning in each stage was different initially no ground flashes were observed in either line until reflectivity increased to 46 dbz and vertically integrated liquid vil increased to 10 kg m22 then ground flash rates remained 1 2 min21 for 1 h most ground flashes in the line of storms near the dryline were negative 18 2cg 3 1cg while most in the leading line were positive 11 1cg 3 2cg a pattern of polarity opposite to what usually has been observed approximately 3 h after radar detected the first storm ground flash rates increased to 5 min21 and remained so for 6 h a mesocyclone formed approximately 30 min after flash rates exceeded 5 min 21 and a few positive ground flashes occurred near it ground flash rates increased briefly to 20 min21 as the mesocyclone dissipated and then remained 10 min21 as a squall line formed along the outflow boundary from the dissipating supercell and produced a stratiform region most ground flashes in this mcs occurred in the convective line and had negative polarity the few ground flashes in the stratiform region tended to be positive 42 1cg 32 2cg during 3 h durin g1ho f themcs ground flash rates decreased and then increased again simultaneously in both the convective and stratiform regions a previously undocumented behavior it is possible that this was caused by updrafts in both the convective line and stratiform region changing at roughly the same time it is also possible that most ground flashes in the stratiform region originated near the convective line and so were influenced by the line overall trends in ground flash density flash relative frequency reflectivity vil and severe hail reports appeared similar as the storm system evolved

transient luminous events above two mesoscale convective systems storm structure and evolution 1 two warm season mesoscale convective systems mcss were analyzed with respect to their production of transient luminous events tles mainly sprites the 20 june 2007 symmetric mcs produced 282 observed tles over a 4 h period during which the storm s intense convection weakened and its stratiform region strengthened tle production corresponded well to convective intensity the convective elements of the mcs contained normal polarity tripole charge structures with upper level positive charge 40 c midlevel negative charge 20 c and low level positive charge near the melting level in contrast to previous sprite studies the stratiform charge layer involved in tle production by parent positive cloud to ground cg lightning resided at upper levels this layer was physically connected to upper level convective positive charge via a downward sloping pathway the average altitude discharged by tle parent flashes during tle activity was 8 2 km above mean sea level msl 25 c the 9 may 2007 asymmetric mcs produced 25 observed tles over a 2 h period during which the storm s convection rapidly weakened before recovering later unlike 20 june tle production was approximately anticorrelated with convective intensity the 9 may storm which also had a normal tripole in its convection best fit the conventional model of low altitude positive charge playing the dominant role in sprite production however the average altitude discharged during the tle phase of flashes still was higher than the melting level 6 1 km msl 15 c based on these results it is inferred that sprite production and sprite parent positive charge altitude depend on mcs morphology

on abandoning the thunderstorm tripole charge paradigm we reexamine the original half century old in situ measurements of simpson and colleagues used to justify the tripole model of charge structure of a thunderstorm that became the paradigm for the charge structure of mature thunderstorms we find that the original measurements violate the criteria of the tripole model in 49 of the cases we also reexamine our soundings of electric field in thunderstorms and mesoscale convective systems in the same way as the original soundings were our soundings do not fit the tripole model in at least 86 of the storms even when we consider only the major features in the electric field profiles our data show noncompliance with the tripole model in 45 of the cases we conclude that we must abandon the paradigm of the tripole charge structure of thunderstorms

electrical structure in thunderstorm convective regions 1 mesoscale convective systems electric field e soundings through convective regions of mesoscale convective systems mcss are examined in this paper ten e soundings through updrafts in mcs convective regions and five soundings in mcs convective regions outside updrafts are used to show that a typical electrical structure exists in this region these 15 e soundings plus one other previously published sounding which is included in this analysis comprise all known soundings in the convective region of mcss the basic charge structure identified in mcs updrafts consists of four charge regions alternating in polarity with the lowest region positive and the highest region negative the basic charge structure outside updrafts in mcs convective regions has six charge regions alternating in polarity with a positive charge region lowest maximum e magnitudes of both polarities are larger and are located at lower heights in soundings outside updrafts compared to those within updrafts excepting the upper positive charge inferred charge regions are shallower and have larger charge densities outside updrafts the center of the main negative charge is lower and warmer outside updrafts 5 5 km 6 2 c than within updrafts 6 9 km 15 7 c these features inside and outside updrafts are incorporated in a new conceptual model of mcs convective region charge structure also an expanded conceptual model is developed using previously published data from other parts of mcss this more complete conceptual model shows the typical electrical charge airflow and reflectivity features in the stratiform region the transition zone and the convective region of midlatitude mesoscale convective systems

error analysis for a long range lightning monitoring network of ground based receivers in europe 1 an experimental long range lightning detection system consisting of a network zeus of six ground based radio receivers has been deployed in europe and has been operated since june 2001 the receivers detect and measure the electromagnetic signal emitted by a lightning source in the very low frequency band between 5 and 15 khz sferics which propagates over thousands of kilometers in the earth ionosphere waveguide in this study lightning location retrievals from the zeus network are compared against more definitive sources in order to investigate issues on long range lightning retrieval accuracy and detection efficiency the validation study is carried out over three regions the u s east coast northwestern atlantic the african continent and within the network spain data originate from the u s national lightning detection network the lighting imaging sensor aboard the tropical rainfall measurement mission satellite and the spanish national lightning network we investigate the nature of the errors involved in the lightning location retrieval and propose a new approach for moderating some of these effects location errors are shown to vary between 40 and 400 km mode at 220 km for very long ranges 5000 km within the network the distance error does not exceed 40 km mode at 20 km random simulation results are shown to be in good agreement with validation data error reduction of 12 or 20 km at long range can be achieved by accommodating for the varying propagation velocities in the sferics wave the long range detection efficiency is shown to have a mode at approximately 20 and a relatively small spread with no obvious deviation from day to night

lightning in the anvils of supercell thunderstorms abstractthis study uses data from the oklahoma lightning mapping array ok lma the national lightning detection network and the norman oklahoma koun prototype weather surveillance radar 1988 doppler wsr 88d radar to examine the evolution and structure of lightning in the anvils of supercell storms as they relate to storm dynamics and microphysics several supercell storms within the domain of the ok lma were examined to determine whether they had lightning in the anvil region and if so the time and location of the initiation of the anvil flashes were determined every warm season supercell storm had some flashes that were initiated in or near the stronger reflectivities of the parent storm and propagated 40 70 km downstream to penetrate well into the anvil some supercell storms also had flashes that were initiated within the anvil itself 40 100 km beyond the closest 30 dbz contour of the storm these flashes were typically initiated in one of three locations 1 coincident with a local reflec

multiple step recrystallization within massive ancient dolomite units an example from the dinantian of belgium south of the caledonian brabant wales massif a more than 200 m thick tournaisian to lower visean replacive dolomite unit can be followed for several hundred kilometres from the boulonnais france to aachen germany field observations of features such as karst cavities occurring at the top of the lower visean dolomite which are filled by lower visean crinoidal limestone indicate that dolomitization and karstification took place during the early visean this early development of the dolomite is in agreement with the presence of stylolites cutting the dolomite fabric the minor element composition of the majority of the dolomites remains almost uniform throughout the entire studied area values for fe mn na and sr are normally in the range 700 4700 ppm 15 400 ppm 80 300 ppm and 50 200 ppm respectively the 13c values range 0 72 to 5 31 o mainly reflect the carbon isotopic composition of the precursor limestones the 18o values in contrast are highly variable ranging from 19 15 to 0 85 o this rather large range of 18o values is explained by multiple step re equilibration recrystallization during progressive burial and subsequent uplift of the dolomites these processes are also responsible for the high 87sr 86sr values of the dolomites which range from about 0 7088 to 0 7098 they are distinctly more radiogenic than lower visean marine carbonates 0 7076 0 7078 correlation however of 18o values or 87sr 86sr ratios with dolomite and or cathodoluminescenec cl textures has not been very successful this suggests that recrystallization may remain unrecognized if only petrographic techniques are used nevertheless certain cl textures can be related to specific interactions with the ambient recrystallizing fluids

horizontal distribution of electrical and meteorological conditions across the stratiform region of a mesoscale convective system abstract five soundings of the electric field and thermodynamic properties were made in a mesoscale convective system mcs that occurred in oklahoma and texas on 2 3 june 1991 airborne doppler radar data were obtained from three passes through the stratiform echo from these electrical kinematical and reflectivity measurements a conceptual model of the electrical structure of an mcs is developed low level reflectivity data from the storm s mature and dissipating stages show typical mcs characteristics the leading convective region is convex forward and the back edge of the stratiform echo is notched inward the maximum areal extent of the low level echo is about 250 km 550 km and the radar bright band is intense reflectivity 45 50 dbz through an area of at least 50 km 100 km the reflectivity above the bright band is horizontally stratified with decreasing intensity and echo top height toward the rear of the system analyses of the velocity data reveal a convective line relative flow struct

a theory for strong long lived squall lines abstract we study herein the mechanics of long lived line oriented precipitating cumulus convection squall lines using two and three dimensional numerical models of moist convection these models used in juxtaposition enable us to address the important theoretical issue of whether a squall line is a system of special long lived cells or whether it is a long lived system of ordinary short lived cells our review of the observational literature indicates that the latter is the most consistent paradigm for the vast majority of cases but on occasion a squall line may be composed of essentially steady supercell thunderstorms the numerical experiments presented herein show that either type of squall line may develop from an initial line like disturbance depending on the magnitude and orientation of the environmental shear with respect to the line with shallow shear oriented perpendicular to the line a long lived line evolves containing individually short lived cells our analysis of this type o

elemental partitioning into mn and fe oxides derived from dolomitic shale hosted pbzn deposits northwest queensland australia abstract exploration for dolomitic shale hosted base metal mineralization in northwest queensland is largely dependent upon geochemical evaluation of ironstones fe oxides because of their abundance in the weathered zone often quantitatively account for most of the base metal content of an ironstone mn oxides are less well developed but provide particularly good hosts for ba zn and pb and hence assume importance where present the mn fe coatings found in stream coatings vigorously scavenge and concentrate solution transported base metals and hence have to be very carefully evaluated when used during exploration however the present survey of base metal contents in gossans and ironstones in northwest queensland has shown that the ba cu p pb ni s and zn contents of the mn and fe oxides can be used to accurately indicate their parent material only ce and co are possibly preferentially incorporated into mn oxides but neither element is a pathfinder for pb zn mineralization development of the mn oxides chalcophanite todorokite lithiophorite and the cryptomelane group incorporating k ca mg ba co zn and pb reflects acid conditions during sulfide oxidation when an ironstone consistently contains mn oxides with greater than 1 pb or 10 zn it can be regarded as derived from pb or zn rich mineralization as ba is often associated with sulfides and facilitates the incorporation of pb into cryptomelane ba without accompanying base metals in a mn oxide implies derivation from base metal barren pyrite and or pyrrhotite cu pb zn al phosphate sulfate and arsenate are all incorporated into fe oxides however only pb which is more strongly partitioned into hematite and al and phosphate which are preferentially incorporated into goethite show clear partitioning between the fe oxide phases the preferential incorporation of phosphate rather than sulfate into an fe oxide makes areas showing higher sulfate contents particularly good targets knowledge of the nature of the distributions of pathfinder elements helps understanding of the associations seen in whole rock analyses and leads to rational application of geochemical data during exploration

geochemical investigations of paleozoic shales and carbonates in the aachen region in the western part of the rheinisches schiefergebirge geochemical investigations were carried out on paleozoic black shales and carbonates in the aachen region primary and secondary metal distributions were determined in selected units of sedimentary rocks by xrf analysis and in stream sediments by aas analysis the primary geochemical pattern and the results of geological studies reveal that frasnian upper devonian black shales and nodular limestones were deposited in a restricted environment under euxinic conditions of a swell and basin facies black shales and nodular limestones are enriched in zn and cu resp possibly indicating stratiform sulphide mineralization geochemical anomalies in stream sediments with increased values of pb zn cd cu co and ni were found in areas of lower paleozoic sedimentary rocks and associated acid intrusives which are known to contain low grade sulphide mineralization of the porphyry copper type

present day precipitation of lead and zinc from groundwaters small quantities of galena and sphalerite are currently precipitating 26m below the surface at the vinemount quarry ontario canada from sulfurous spring waters issuing from carbonates of the lockport formation at the spring orifices these sulfides are present in both fracture coatings and an associated black sludge these precipitates are overlain by a crust rich in native sulfur the mineralogy of the precipitates and the chemistry of waters taken from three consistent spring horizons indicates that downward moving meteoric groundwaters leach metals from the host rocks and precipitate galena and sphalerite on encountering h2s rich waters at the water table while our observation of the transport and deposition of lead and zinc by shallow groundwaters lends support to intra karstic models for the direct precipitation of galena and sphalerite it also enables us to propose that many carbonate hosted pb zn deposits of differing theories of origin may have been enriched during periods of uplift

evolution of cloud to ground lightning characteristics and storm structure in the spearman texas tornadic supercells of 31 may 1990 abstract on 31 may 1990 four tornadic supercell storms formed sequentially near the intersection of a dryline and an outflow boundary in the northern texas panhandle staccato lightning flashes which have been hypothesized to be positive ground flashes were observed beneath the anvil of one storm during the most violent tornado that the storm produced evidence was found from a lightning mapping system that at least some of the staccato flashes were negative ground flashes although the four supercell storms on this day formed in approximately the same area traveled over roughly the same region and produced tornadoes and large hail the relationship between the genesis and evolution of tornadoes and the polarity and flash rates of ground flashes varied widely as in previous studies the second of the supercell storms had low precipitation supercell characteristics the third and fourth did not in previously studied storms ground flash activity in low precipitation supercell storms has always bee

sulfur bearing magmatic accessory minerals almost all magmas contain sulfide or sulfate bearing phases in most natural samples the sulfur bearing phase is a sulfide which typically is pyrrhotite fe1 x s or pyrite fes2 although chalcopyrite cufes2 pentlandite fe ni 9s8 sphalerite zns or molybdenite mos2 may be present as well sulfate minerals are rare at magmatic conditions and anhydrite caso4 is the most common other magmatic so4 bearing minerals include the sodalite group minerals hauyne simplified formula na ca 4 8 al6si6 o s 24 so4 cl 1 2 scapolite minerals silvialite ca na 4al6si6o24 so4 co3 and s bearing apatite ca5 po4 3 f cl oh barite baso4 has been mentioned in rare cases marchev 1991 sulfur bearing minerals usually constitute a negligible fraction of the mineral assemblage in magmatic rocks and thus can be classified as accessory minerals the crystallization of sulfide sulfate and s bearing minerals strongly depends on melt composition temperature and pressure and the s speciation in melt which in turn is strongly dependent on the prevailing oxygen fugacity baker and moretti 2011 this volume wilke et al 2011 this volume irrespectively of the low abundance of s bearing minerals the evolution of sulfur in magmas may be evaluated from the occurrence of sulfides and sulfates these minerals are critical for estimating the activity of various sulfur bearing species in magmas and can be used to constrain the oxygen fugacity and the s concentration in the melt e g pre eruptive sulfur concentration in melts the presence of either sulfide or sulfate in silicate melt indicates that the predominant dissolved sulfur species in the melt are s2 or s6 respectively typically one of these species is dominant but there are conditions where s2

electrical structure in thunderstorm convective regions 3 synthesis in this paper results from nearly 50 electric field soundings through convective regions of mesoscale convective systems mcss isolated supercells and isolated new mexican mountain storms are compared and synthesized these three types of thunderstorm convection are found to have a common basic electrical structure within convective updrafts the basic charge structure has four charge regions alternating in polarity and the lowest is positive outside updrafts of convection there are typically at least six charge regions alternating in polarity and the lowest is again positive among the three storm types there are differences in the heights and temperatures at which the basic four charge regions are found in updrafts the height temperature of the center of the main negative charge region averages 6 93 km 16 c in mcs convective region updrafts 9 12 km 22 c in supercell updrafts and 6 05 km 7 c in new mexican mountain storm updrafts in updraft soundings through all three storm types the center height of the main negative charge region increases with increasing average balloon ascent rate and updraft speed at a rate of about 0 3 km per 1 m s 1 with a correlation coefficient of 0 94 a schematic illustrates the basic four and six charge structure for thunderstorm convective regions and it is offered as an improved model for thunderstorm charge structure

cloud to ground lightning in linear mesoscale convective systems recently three distinct archetypes for midlatitude linear mesoscale convective systems mcss have been identified those comprising convective lines with trailing stratiform precipitation ts leading stratiform precipitation ls and parallel stratiform precipitation ps while cloud to ground cg lightning in ts mcss has received a great deal of study in recent years linear mcss exhibiting leading or parallel stratiform precipitation have received comparatively little attention this paper documents the arrangement and frequency of cg lightning for four ls and four ps mcss that occurred during may 1996 and may 1997 on average the ls cases bore some similarity to previously studied ts mcss they produced predominantly positive cg lightning 1cg early in their lifetimes concomitant with convective precipitation and late in their lifetimes concomitant with stratiform precipitation in contrast with previously published results for mcss in general the ls mcss in the present study overall had relatively low negative cg 2cg flash densities yielding higher percentages of 1cgs than other mcs archetypes while the ps systems had higher average flash densities than the ls systems they did not exhibit prolonged 1cg modes early in their lifetimes and they produced a lower overall fraction of 1cgs notably the presence of line parallel flow may render a somewhat unique electrical character in ps systems in particular the ps mcss in this study exhibited enhanced cg lightning in the vicinity of decaying convective cells that were embedded within their stratiform precipitation regions

carbonate sedimentation and diagenesis associated with mg ca chloride brines the permian san andres formation in the texas panhandle abstract the san andres evaporitic sequence in the palo duro basin includes several thick carbonate units in its lower part and many thin units in its upper part evaporites are concentrated in the northern part of the northern shelf of the midland basin and carbonates predominate to the south within the palo duro basin the carbonates in the lower part of the sequence differ from those in the upper part in containing skeletal lithofacies and in having lower mn fe and terrestrial organic content the br content in halite in the lower part of the sequence is consistently high whereas halite in the upper part is commonly br depleted the sr content in dolomite calcite and anhydrite and 18o values are about the same in the en ire san andres sequence in the palo duro basin depleted 13c values in dolomite and low pristane phytane ratios occur toward the south na cl and k cl ratios attributed to liquid inclusions in almost all carbonates are characteristic of marine brines evaporated beyond halite saturation na in the dolomite lattice is generally low and increases from north to south at the same stratigraphic levels the lower part of the formation was deposited in a broad shelf basin or lagoon sufficiently deep to maintain long periods of steady state circulation during which little halite dissolution and no potash magnesia mineral precipitation occurred the upper part of the formation was deposited in smaller water bodies sensitive to fluctuations in inflow of marine water as well as meteoric water diagenesis of the carbonates occurred in contact with saline mg ca chloride brines evolved through anhydrite and halite precipitation skeletal mold formation anhydrite cementation dolomitization and high sr calcite cementation associated with celestite are all cogenetic products of such a brine rock interaction 18o of dolomite calcite and chert indicates apparent equilibrium relationships with the same solution temperatures have never exceeded 40 to 45 c and imply the 18o of such a solution to be about 3 the somewhat depleted 18 up o composition of the proposed halite saturated brine resulted from the reversal in the dependence of 18o on increased evaporation in highly saline brines the proposed diagenetic model implies that following early diagenetic processes the rock sequence remained as a closed but compacting system unchanged by later fluid introduction low sr values in dolomite are indicative of recrystallization and not fresh water diagenesis

experimental constraints on the mobility of rhenium in silicate liquids abstract the volatization of rhenium re from melts of natural basalt dacite and a synthetic composition in the cao mgo al2o3 sio2 system has been investigated at 0 1 mpa and 1250 1350 c over a range of fo2 conditions from log fo2 10 to 0 68 experiments were conducted using open top pt crucibles doped with re and yb analysis of quenched glasses by laser ablation inductively coupled plasma mass spectrometry la icp ms normal to the melt gas interface showed concentration profiles for re to which a semi infinite one dimensional diffusion model could be applied to extract diffusion coefficients d the results show re diffusivity in basalt at 1300 c in air is log dre 7 2 0 3 cm2 s and increases to log dre 6 6 0 3 cm2 s when trace amounts of cl were added to the starting material at fo2 conditions below the nickel nickel oxide nno buffer re diffusivity decreases to log d re reducing 7 6 0 2 cm 2 s and to log d re dacite 8 4 0 2 cm 2 s in dacitic melt in the cmas composition log d re cmas 7 5 0 1 the diffusivity of re is comparable to ar and co2 in basalt at 500 mpa favoring its release as a volatile our results support the contention that subaerial degassing is the cause of lower re concentrations in arc type and ocean island basalts compared to mid ocean ridge basalts

zinc speciation in mining and smelter contaminated overbank sediments by exafs spectroscopy overbank sediments contaminated with metalliferous minerals are a source of toxic metals that pose risks to living organisms the overbank sediments from the geul river in belgium contain 4000 69 000 mg kg zn as a result of mining and smelting activities principally during the 19th century three main zn species were identified by powder zn k edge exafs spectroscopy smithsonite znco3 tetrahedrally coordinated sorbed zn sorbed ivzn and zn containing trioctahedral phyllosilicate smithsonite is a primary mineral which accounts for approximately 20 60 of the zn in sediments affected by mining and smelting of oxidized zn ores mostly carbonates and silicates this species is almost absent in sediments affected by mining and smelting of both sulphidic zns pbs and oxidized ores presumably because of acidic dissolution associated with the oxidation of sulphides as suggested by the lower ph of this second type of sediment ph cacl2 7 0 for the first type thus sulphide minerals in sediment deposits can act as a secondary source of dissolved metals by a chemical process analogous to acid mine drainage the sorbed ivzn component ranges up to approximately 30 with the highest proportion occurring at ph cacl2 7 0 as a result of the readsorption of dissolved zn2 on sediments constituents kerolite like zn rich phyllosilicate is the major secondary species in all samples and in some the only detected species thus providing the first evidence for pervasive sequestration of zn into this newly formed precipitate at the field scale

re and os concentrations in arc basalts the roles of volatility and source region fo2 variations olivine and spinel compositions major elements including ferric and ferrous iron s re and os contents have been measured for a suite of primitive most 6 wt mgo basalts from the trans mexican volcanic belt tmvb including the western mexican volcanic belt the michoacan guanajuato volcanic field sierra chichinautzin pico de orizaba region palma sola san martin tuxtlas and the eastern alkaline province eap sulfur contents at sulfide saturation were calculated to determine whether the measured s contents are representative of sulfide saturated liquids most of the samples have s contents much lower than expected for sulfide saturation a few have higher contents than calculated perhaps due to the presence of sulfate in the measured total sulfur i e more oxidized samples comparison of the tmvb samples along with previously analyzed morb oib babb and arc samples reveals a continuum of re and os contents that is best explained by variation in oxygen fugacity and thus sulfide stability in the source region high re and os magmatic suites are best explained by derivation by melting of oxidized mantle where sulfide is no longer stable and re and os behave incompatibly whereas low re and os magmatic suites are derived from melting of relatively reduced mantle where sulfide is stable and re and os behave compatibly intermediate examples abound and arc magmas span a wide range of re and os concentrations due to variation of fo2 in the source during genesis of arc magmas low re magmatic suites are furthermore potentially affected by volatility which can lower re by a factor of 3 5

spheroidal dolomites in a visean karst system bacterial induced origin spheroidal dolomite crystals occur in the karstified top of a dinantian dolomite sequence in eastern belgium the spheroidal dolomite crystals are best developed at the base of the karst system the dolomite crystals are characterized by a spherulitic or dumb bell inclusion pattern and are overgrown by dolomite cements with a rhombohedral outline they are considered to be bacterially related precipitates based on 1 textural similarities with documented bacteriogenic precipitates 2 the presence of bacterial microspheres and framboidal pyrite embedded within the dolomite and 3 their general geological setting the geochemical characteristics of the dolomites and associated minerals support a bacterial origin the ubiquity of framboidal pyrite depleted in 34s 34s 22 4 to 25 5 ocdt testifies to a period of bacterial sulphate reduction the isotopic composition of the spheroidal dolomites 13c 2 4 to 3 2 opdb and 18o 3 8 to 3 4 opdb suggest a contribution from oxidized organic carbon produced during bacterial sulphate reduction sulphate reduction may also result in a concomitant 18o depletion if the system is nearly closed it is however evident from the sulphur isotopic composition of associated framboidal pyrite that the system was fairly open the 18o depletion of the spheroidal dolomite crystals 18o 3 8 to 3 4 opdb and their occurrence adjacent to and within karst cavities suggests a mixing zone origin with a significant proportion of freshwater in it the rhombohedral cement overgrowths have calculated 18o values in the range of 0 to 5 3 opdb which reflect precipitation from normal to slightly evaporated contemporaneous seawater

two simultaneous charge structures in thunderstorm convection 1 a pair of simultaneous horizontally displaced thunderstorm electric field soundings are used to investigate an existing conceptual model of thunderstorm charge structure the soundings show that two different vertical charge structures one in the updraft and one outside the updraft can exist at the same time inside a storm as depicted in the existing model the data suggest that the two charge structures can be relatively close together since the soundings are separated by only 3 to 8 km horizontally in the convective region of the storm horizontal extent of the charge structures is estimated to be at least 4 km 4 km the differences in the two charge structures are coincident with substantial differences over this same 3 to 8 km horizontal distance in the reflectivity structure updraft speed and lightning activity of the convection the nonupdraft sounding was made through the intense reflectivity core found at middle levels in the convection additional electric field complexity and additional charge regions were found in the nonupdraft sounding and the lightning related electric field changes tended to be larger in magnitude and more numerous in that sounding than in the updraft sounding

serial soundings of electric field through a mesoscale convective system five partial balloon soundings of electric field and thermodynamics were made in a mesoscale convective system mcs in 1998 data were gathered in an updraft and outside updrafts within the convective region in the transition zone and in the stratiform cloud region in the first sounding the maximum and average inferred updraft speeds 27 and 15 m s 1 are the largest found to date in soundings through mcs convection as in previous measurements the electric field profile is simpler and fewer charge regions are inferred within the updraft than elsewhere together the first four soundings support in most details a previously published conceptual model of mcs electrical structure from the convective region updraft to the transition zone two exceptions within the soundings were found these involve opposite polarity of the lowest two charge regions in the transition zone cloud and additional complexity above the main negative charge region the earlier conceptual model also showed possible connections between charge regions across an mcs but those were based on soundings through many different mcss the first four soundings presented herein provide stronger evidence for three to five similar charge regions across the front of this mcs the sounding through the stratiform cloud region was atypical and does not fit the conceptual model and no connections to charge regions in the rest of the mcs are obvious two soundings presented from a second mcs indicate that the upper three charge regions in the transition zone are connected to the stratiform cloud as depicted in earlier conceptual models

rapid intensification of a sheared tropical storm abstract a weak tropical storm gabrielle in 2001 experienced a 22 hpa pressure fall in less than 3 h in the presence of 13 m s 1 ambient vertical wind shear a convective cell developed downshear left of the center and moved cyclonically and inward to the 17 km radius during the period of rapid intensification this cell had one of the most intense 85 ghz scattering signatures ever observed by the tropical rainfall measuring mission trmm the cell developed at the downwind end of a band in the storm core maximum vorticity in the cell exceeded 2 5 10 2 s 1 the cell structure broadly resembled that of a vortical hot tower rather than a supercell at the time of minimum central pressure the storm consisted of a strong vortex adjacent to the cell with a radius of maximum winds of about 10 km that exhibited almost no tilt in the vertical this was surrounded by a broader vortex that tilted approximately left of the ambient shear vector in a similar direction as the broad precipitation shield this st

sulfide globules in mid ocean ridge basalts morb and the effect of oxygen abundance in feso liquids on the ability of those liquids to partition metals from morb and komatiite magmas the coexistence of sulfide liquids or more accurately fe s o liquids with silicate liquids in a variety of magma systems is well known as is the ability of immiscible fe s o liquids to segregate ni cu and platinum group metals into orebodies evidence for association of fe s o liquids with magmas that form mid ocean ridge basalts morb comes from sulfide globules in basalt glass from siqueiros fracture zone east pacific rise three fracture zones in the indian ocean lau basin and 23 previously published oceanic localities approximately 40 of the sulfur originally present in magma at siqueiros fracture zone exsolves as a sulfide liquid during fractional crystallization virtually all of the cu and 20 of the ni originally in the magma is extracted by the sulfide liquid significant variations in the ability of fe s o liquids to partition ni cu exist among morb and other mafic magmas such as komatiites and layered mafic intrusions nernst partition coefficients sulfide to silicate melt dsl are 2 3 times higher for ni in morb than in komatiite and 5 times higher for cu reasons for this variation are not entirely clear but a possible contributing factor is that fe s o liquids in morb appear to have a higher oxygen content than those in komatiites that fe s o liquids associated with morb magma are oxygen rich is suggested by low observed values at siqueiros fracture zone for the ni fe exchange coefficient kd3 1 21 4 56 kd3 feni olivine feni sulfide it has been previously shown that natural magmatic fe s o liquids are rich in o2 o s o is apparently always greater than 0 49 and that kd3 is inversely correlated with o s o kd3 values below 12 would result from fe s o liquids with o s o 0 49 kd3 value of 20 would be impossible values from 12 to 20 would be unlikely because they would require an fe s o liquid poor in o2 this argument for low kd3 in magmas is strengthened by the low kd3 values of morb whose globules are inarguably of magmatic origin kd3 in komatiites is higher than in morb indicating a lower oxygen fugacity in komatiite magma and varies from 5 to 20 with values of 20 coming from highly metamorphosed komatiites fleet and macrae argued on the basis of experimental results that kd3 values of 20 could not have resulted from magmatic processes but might have come from metamorphism under oxygen deficient conditions

a diagnostic modelling study of the trailing stratiform region of a midlatitude squall line abstract a kinematic model with continuity equations for sensible heat water vapor cloud water cloud ice rain snow and graupel is used to determine the steady state thermodynamic and microphysical processes associated with the observed mesoscale air motion fields in the trailing stratiform region of the 22 may 1976 oklahoma squall line two versions of the observed air motions are used a low resolution but areally extensive flow pattern derived from the composite sounding data of ogura and liou and a high resolution but less areally extensive flow field obtained from the dual doppler radar analysis of smull and houze model calculations based on the high resolution doppler derived mesoscale air motions show that the location and horizontal scale of the region of most intense stratiform precipitation are determined by the pattern of horizontal transport and fallout of snow and low density graupel particles advected into the stratiform region from the leading line of convective cells the stratiform

electrical and multiparameter radar observations of a severe hailstorm using data from the 11 cm csu chill multiparameter radar the simultaneous evolution of the radar inferred precipitation structure and electrical characteristics of a severe hailstorm is investigated we compare the substorm point discharge current intracloud ic lightning flash rate cloud to ground cg lightning flash rate ground strike location and flash polarity to the progression of precipitation types and amounts this study is unique in that it presents multiparameter radar observations of a thunderstorm complex which exhibited an extremely high ic to cg ratio ic cg 20 70 and predominantly positive cg lightning over 74 after it became severe producing large hail and weak tornadoes in particular we investigate the reported relationship between large hail and positive cg lightning although a direct correlation is found between a rapid increase in ic cg the first positive cg lightning flashes and the initial production of hail aloft the temporal and spatial behavior of large hail and positive cg lightning appear to be anticorrelated as broad peaks in the positive cg flash rate lag relative maxima in the fallout of large hail by up to 30 min the majority of positive ground strikes were adjacent to the main precipitation core in a region of light rain and little or no hail at the surface aloft radar data indicated that ice crystals were aligned vertically in a strong electric field corona point observations at the surface indicate that these regions adjacent to the convective core were characterized by net positive charge aloft possible mechanisms to explain these observations are discussed

origins of positive cloud to ground lightning flashes in the stratiform region of a mesoscale convective system 1 the origins of positive cloud to ground cg lightning in the stratiform region of a leading line trailing stratiform mesoscale convective system mcs are investigated platforms include radars nldn data and a vhf 3 d lightning mapping system this study examines a small asymmetric mcs that occurred near the colorado kansas border in june 2000 in this storm 39 of the 269 cgs produced over a nearly 5 hour period came to ground within the stratiform region of these 30 initiated in the leading convective line and propagated rearward before coming to ground nine other cgs originated within the stratiform region stratiform cgs were observed to propagate mostly horizontally through vertically thin layers the observations suggest that stratiform charge is a conduit for cg lightning from the convective line and can initiate cgs as well

multiscale analysis of a mature mesoscale convective complex abstract a multiscale analysis reveals diverse atmospheric structure and processes within a mesoscale convective complex mcc observed during the oklahoma kansas preliminary regional experiment for storm central pre storm experiment this midlatitude system was the second in a series of four mccs that developed and traveled along a quasi stationary frontal zone over the central united states on 3 4 june 1985 objectively analyzed mesoscale upper air soundings encompassing the mcc are interpreted in tandem with more detailed dual doppler radar measurements that disclose the storm s internal airflow and precipitation structure the mature mcc is found to include a variety of local environments and associated weather ranging from tornadic thunderstorms to more linear convective bands and widespread chilling rains a corresponding spectrum of mesoscale ver6cw motion profiles is documented these findings are related to previous composite based portrayals of mccs as well as detailed case studies of simple

heavy metal contamination in overbank sediments of the geul river east belgium its relation to former pb zn mining activities overbank sediments of the geul river east belgium are highly contaminated by the heavy metals pb zn and cd due to former pb zn mining activities in the drainage basin geochemical variations in vertical overbank sediment profiles sampled 1 km north of the mine tailings of plombieres allow metal fluxes back to the 17th century to be reconstructed the vertical profiles are subdivided into three major units corresponding to different industrial periods based on sedimentological criteria as well as on the distribution of contaminants alluvial sediments with the highest heavy metal concentrations correspond to the major period of mining activity of the 19th century the fact that zn mining at the la calamine open mine started before large scale mining of the pbs zns subsurface exploitations is reflected in the vertical profiles by an increase in zn content before a marked increase in pb and cu the regional extent of contamination in the alluvial deposits was evaluated on the basis of the geochemical analysis of sediments at depths of the 0 20 cm and 80 100 cm most of the upper samples are extremely contaminated significant local variations in heavy metal concentration in the lower samples are interpreted in terms of which overbank sediment horizon has been sampled at a depth of 80 100 cm this indicates that blind sampling of overbank sediments to characterize the degree of contamination in shallow boreholes can give very erratic results

lithogeochemical patterns around pb zn mineralizations in dinantian carbonate rocks of eastern belgium the lithogeochemical distribution patterns of mg sr na zn pb fe mn k corg organic matter and ir insoluble residue in the dinantian limestones and dolomites from the eastern part of belgium have been studied dinant and verviers synclinorium comparison of geochemical data of non mineralized strata revealed higher background values in the strata of the verviers synclinorium where pb zn mineralizations occur in this area a relation may exist with the metallogenetic district herve vesdre theux district proposed by dejonghe 1985b however the higher background values also could relate to the more restricted sedimentation conditions in the verviers synclinorium as opposed to the more open marine conditions in the dinant synclinorium the influence of mineralization on the geochemistry of limestones is limited and unpredictable in dolomites however the effect can be important in these rocks the lithogeochemical distribution of zn pb and mn can be subdivided into three populations i e a regional background a local high background and a halo population the higher trace element concentrations in the halo population is caused by the existence of disseminated sulfide minerals sphalerite galena and pyrite and zn bearing goethite mainly pseudomorphs after pyrite and mn oxides the sulfides relate to the ore emplacement in the local high background only the zn bearing oxides occur their presence and thus the development of the local high background relates to weathering processes

fluid melt partitioning of re mo w tl and pb in the system haplobasalt h2o cl and the volcanic degassing of trace metals abstract the partition coefficients kd x f m of re mo w tl and pb between fluid h 2 o cl and a haplobasaltic melt in the cao mgo al 2 o 3 sio 2 system were measured between 1300 and 1400 c at 1 gpa and fluid chlorine molarities from 7 7 to 27 mol l dissociation of hydroxides added to a trace metal doped oxide powder produced a fluid phase in equilibrium with melt at the run conditions the kd x f m values were determined by mass balance of trace metals added with those determined in glass from the run products at 1300 c and fluid molarity of 7 7 mol l kd re f m 9 8 1 8 kd mo f m 11 8 1 6 kd w f m 3 7 1 6 kd tl f m 4 5 1 4 and kd pb f m 2 4 1 8 both mo and re were shown to partition most strongly into the fluid at all temperatures and fluid chlorinities at 1400 c kd pb f m and kd tl f m were the only elements showing any correlation with fluid chlorinities at 1400 c re and mo completely partitioned into the fluid and thus our calculated kd re mo f m are minima controls on fluid melt partitioning are explored in detail calculated values of kd re tl pb f m were combined with the diffusivity of these elements in a 1 d bubble growth model to evaluate the change in metal concentrations and metal ratios expected during the degassing of magma the model results were compared with emanation coefficients for trace metals from natural volcanoes the magnitudes of the modeled re tl and re pb in fluids using the diffusivity and partitioning values at 1300 c and the lowest fluid chlorinities were less than that observed from their emanation coefficients

observation of thunderstorms by multilevel electric field measurement system and radar during the summer of 1992 an experiment was conducted in southwestern france close to the pyrenees at the centre de recherches atmospheriques cra in order to study the evolution of the electric field measured at several levels below thunderclouds we used a field mill flush to the ground and four field sensors suspended from an insulated cable and distributed between 0 and 48 m these altitude sensors separately measure the ambient electric field and the field created by the sensor itself the rabelais millimetric radar provides reflectivities and doppler velocities of cloud and rain systems meteorological data like wind velocity humidity temperature and rainfall rate are recorded at the site two storm intervals are studied one on july 30 and one on august 6 both examples give an idea on how the electric field signature during the development or advection of a convective cloud can be different at the ground and at altitudes of a few tens of meters the maxima in the electrostatic activity are visible only on the altitude electric field evolution the maximum value of the electric field between lightning flashes close to 30 kv m 1 is detected at 48 m above ground a vertical gradient of the electric field is observed in this 48 m thick layer especially when the field is high the upward progressive development of this gradient is interpreted in terms of a local charge generated by corona at the ground and rising by conduction the average charge density in the whole layer reaches around 5 nc m 3 between lightning flashes when the field keeps large values of the same polarity this density is weaker when the electric field has taken large values of both polarities long periods of different electrical activity are observed during both storms those with large electrostatic fields without any lightning flash and those with lightning activity the former are associated with a thick stratiform cloud structure possibly with strong radar echoes above the melting level but without rain reaching the ground the latter are associated with rain reaching the ground close to the measurement area these observations suggest that the water liquid phase could play an important role in lightning initiation

the role of convectively generated rear inflow jets in the evolution of long lived mesoconvective systems abstract in this study the structure of convectively generated rear inflow jets and their role in the evolution of long lived mesoconvective systems are investigated through an analysis of idealized three dimensional simulations using a nonhydrostatic cloud model rear inflow jets are generated within these systems in response to the upshear tilting of the convective circulation as the horizontal buoyancy gradients along the back edge of the expanding system create a circulation that draws midlevel air in from the rear within this framework a wide range of rear inflow strengths and structures are produced depending on the magnitude of the ambient convective available potential energy cape and the vertical wind shear in general for environments characterized by weak to moderate vertical wind shear and weak to moderate cape the rear inflow jet descends and spreads along the surface well behind the leading edge of the gust front and the subsequent convective activity becomes weaker however for e

behavior of re during magma fractionation an example from volcan alcedo galapagos 1988 many applications in geo and cosmochronology and these sequences are more diycult to interpret becausemantle and crustal studies in mantle and crustal melting these materials could potentially disturb trace elementenvironments re is thought to be incompatible and os abundances from the values controlled solely by crystal

electric fields and charges near 0 c in stratiform clouds abstract earlier studies of mesoscale convective system stratiform regions have shown that large electric fields and charge densities are found near the 0 c level here 12 soundings of the electric field were analyzed through the 0 c level in various types of electrified stratiform clouds for each electric field sounding the thermodynamic sounding and supporting radar data were also studied for comparison five soundings not from stratiform clouds were included charge densities were found at or near 0 c in the stratiform clouds of at least 1 nc m 3 in eight of the soundings and four of those had charge densities of at least 2 nc m 3 of the stratiform soundings 11 had an electric field magnitude of greater than 50 kv m 1 near 0 c and 7 of those had an electric field magnitude of at least 75 kv m 1 the evidence suggests that melting may be the primary cause of the charge density found at and below 0 c in electrified stratiform clouds in all 12 of the stratiform soundings positive charge density w

analysis of a small vigorous mesoscale convective system in a low shear environment part i formation radar echo structure and lightning behavior the evolution of a small vigorous mesoscale convective system mcs over northern alabama is described using doppler radar goes satellite surface mesonet lightning and sounding data the mcs formed near noon in a relatively unstable environment having weak synoptic forcing and weak shear the initiation of separate lines and clusters of deep convection occurred in regions exhibiting cumulus cloud streets horizontal variations in stratocumulus cloud cover and variations in inferred soil moisture mcs growth via merger of storms within clusters and lines and among the clusters was accomplished largely through intersection of storm scale and mesoscale outflow boundaries the mcs maximum anvil area 60 000 km2 at 220 k and lifetime 8 h were about 50 that of the typical great plains mesoscale convective complex mcc despite its smaller size this mcs displayed many aspects that typify the mostly nocturnal great plains mcs the precipitation output was highly variable due to the transient nature of the intense convective elements many of which produced microbursts the radar measurements documented the formation of a stratiform region along the trailing side of an intense convective line this stratiform region formed as decaying convective cores coalesced rather than through advection of precipitation particles directly from the convective region combined goes ir imagery and radar reflectivity analyses within the stratiform region show a sinking anvil cloud top in the presence of increases in the vertical radar reflectivity gradient within the cloud during the maturation of the stratiform region during its intense developing stages the mcs generated a peak cloud to ground cg flash rate of 2400 h 21 comparable to rates produced by larger mccs early on positive cg flashes were most prevalent around intense convective core regions exhibiting strong divergence at anvil level during the latter stages the emergence of positive cg was coincident with the formation of a prominent radar bright band within the stratiform region thus a bipole was established but its length was quite short at approximately 50 km 25 50 of the distance documented in other mcss

electrical structure in thunderstorm convective regions 2 isolated storms electric field e soundings through the convective regions of two types of isolated thunderstorms are examined analysis of seven soundings through strong updrafts of isolated supercell storms show that the basic e structure there has three e peaks a positive peak near 8 km height a negative peak near 10 5 km and a positive peak near 12 km strong updraft soundings are those with average balloon ascent rates in excess of 10 m s 1 the basic charge structure in strong updrafts of supercells has four charge regions of alternating polarity the lowermost charge is positive between about 4 and 8 km and the uppermost region is negative all the supercell updraft soundings are incomplete due to balloon burst or lightning induced instrument destruction below cloud top six supercell soundings that ascended outside strong updrafts are used to show that the e and charge structures there are more complex than within the strong updrafts analysis of 15 new or previously published soundings through small new mexican mountain thunderstorms indicates that the basic e structure in or near their convective cores consists of three e peaks a lower positive peak at about 5 km height a midlevel negative peak near 6 5 km and an upper positive peak near 9 5 km the basic charge structure near the center of new mexican storm convection has four charge regions alternating in polarity with a positive charge region lowest soundings in new mexican convection that did not ascend near the convective cores show more complex e profiles and charge structures

copper enrichment in arc magmas controlled by overriding plate thickness the characteristics of magmas typically associated with porphyry copper deposits are thought to be imparted in the mantle statistical assessment of over 40 000 geochemical analyses of magmatic rocks formed in subduction zones worldwide however shows that the characteristics of these magmatic rocks are systematically controlled by the thickness of the arc crust

gold solubility in oxidized and reduced water saturated mafic melt abstract we have performed experiments to evaluate au solubility in natural water saturated basaltic melts as a function of oxygen fugacity experiments were carried out at 1000 c and 200 mpa and oxygen fugacity was controlled at the fayalite magnetite quartz fmq oxygen fugacity buffer and fmq 4 all experiments were saturated with a metal chloride aqueous solution loaded initially as a 10 wt nacl eq fluid the stable phase assemblage at fmq consists of basalt melt olivine clinopyroxene a single phase aqueous fluid and metallic au the stable phase assemblage at fmq 4 consists of basalt melt clinopyroxene magnetite spinel solid solution a single phase aqueous fluid and metallic au silicate glasses i e quenched melt and their contained crystalline material were analyzed by using both electron probe microanalysis epma and laser ablation inductively coupled plasma mass spectrometry la icp ms measured au concentrations in the quenched melt range from 4 8 g g 1 to 0 64 g g 1 at fmq 4 and 0 54 g g 1 to 0 1 g g 1 at fmq the measured solubility of au in olivine and clinopyroxene was consistently below the la icp ms limit of detection i e 0 1 g g 1 these melt solubility data place important limitations on the dissolved au content of water saturated cl and s bearing basaltic liquids at geologically relevant fo2 values the new data are compared to published experimentally determined values for au solubility in dry and hydrous silicate liquids spanning the compositional range from basalt to rhyolite and the effects of melt composition oxygen fugacity pressure and temperature are discussed

the magnetite crisis in the evolution of arc related magmas and the initial concentration of au ag and cu the association of large au cu ag ore deposits with convergent margins is commonly attributed to the higher content of chalcophile elements in the parental magmas generated at subduction zones compared with mid ocean ridges we present new geochemical data for arc like relatively oxidized mantle derived basalt to rhyolite magmas from the pual ridge and vicinity eastern manus basin which show that the initial abundances of base and precious metals in the parental basalts are similar to those of mid ocean ridge basalt morb the contents of au cu and ag are built up in the evolving pual ridge liquids to levels considerably in excess of those in morb because unlike morb they are not saturated in a sulfide phase which is a consequence of their being more oxidized than morb the behaviour of s during the evolution of the pual ridge magmas is obscured by late stage so2 loss during eruption but we show that it may be inferred by using se as a proxy because this element follows s closely during magmatic evolution except it is not lost during low pressure near sea floor degassing the onset of magnetite fractionation at 60 wt sio2 and an mg number of 40 is accompanied by an abrupt decrease in the contents of au cu and ag previously attributed to separation of cu au rich fluid which is also shown by se implying that magnetite fractionation triggers sulfide saturation petrological modelling reveals that the amount of magnetite fractionation involved is sufficient to convert most of the s originally dissolved in the magma as sulfate so42 to sulfide s2 triggering saturation in a cu rich sulfide phase tentatively identified as bornite cu5fes4 this sulfide phase sequesters au and ag elements with the same valence as cu in sulfides but not other potentially chalcophile elements such as ni re and pt which suggests that the phase is crystalline rather than an immiscible sulfide melt the relatively high contents of cu and au characteristic of evolved convergent margin magmas requires no enrichment from subducted material instead the association of major cu au deposits with convergent margin magmatism results specifically from the process of magmatic evolution under oxidizing conditions this same property also leads to early magnetite fractionation triggering the abrupt saturation in the cu rich sulfide hence the easily recognizable trend of magmatic evolution under oxidizing conditions i e the sharp drop in chalcophile element concentrations may be an exploration guide to economic au ag cu provinces or a crucial pre enrichment step in the formation of such deposits the decrease in p2o5 and sr at the same stage in the fractionation sequence 60 wt sio2 indicates that saturation in apatite is concomitant with magnetite sulfide saturation in the eastern manus basin

petrography and geochemistry of the belle roche breccia lower visean belgium evidence for brecciation by evaporite dissolution the lower visean belle roche breccia east belgium displays a number of features that indicate brecciation by evaporite dissolution collapse the sharp lower contact of the breccia the gradual transition into the overlying strata the presence of semi continuous beds within the breccia giving it a crude stratification and the existence of several types of calcite dolomite and silica evaporite pseudomorphs furthermore the majority of the breccia fragments indicates hypersaline to lagoonal sedimentation conditions most of these fragments display an interlocking fabric the interpretation is also supported by the existence of continuous evaporite beds replaced by carbonates calcite and dolomite both under and overlying the breccia the brecciation history is characterized by gradual subsidence multiple brecciation episodes are recognized and are best seen in the lower breccia which underwent at least two major brecciation episodes here brecciated and veined breccia fragments occur within a microsparite neomorphosed mud matrix brecciation of these strata was due to the dissolution of interlayered evaporites the second brecciation event relates to infiltration of meteoric water and to the dissolution of the remaining evaporites this infiltration was probably triggered by the orogenic event at the end of the visean sudetic orogenic phase the whole breccia was finally cemented by a blocky calcite the different lithologies and cements were characterized by their trace element mg sr na fe mn k insoluble residue and organic matter content carbon oxygen isotope data of the cements and replaced evaporite layers helped to place the multiple collapse episodes within a general diagenetic model solution reprecipitation processes within the original aragonite dominated mud fragments as well as in the early diagenetic dolomite fragments have been recognized the geochemical data show that these transformation processes occurred in equilibrium with the same fluid these processes may have occurred within a freshwater lens very early in the diagenetic evolution or under shallow burial conditions cementation of blocky calcite occurred in a meteoric realm under burial conditions

electrical structure and updraft speeds in thunderstorms over the southern great plains we have acquired 11 balloon soundings of the electric field and thermodynamics in large and sometimes severe and tornadic thunderstorms over the southern great plains the ascent rates of the balloons were used to divide the soundings into weak and strong updrafts all 11 soundings had magnitudes of charge densities and thicknesses of charge regions similar to those reported previously in small thunderstorms the five weak updraft soundings had complex charge structures of 7 9 charge regions below 10 km altitude the magnitude of the maximum measured electric field in these soundings was 100 150 k v m 1 the four soundings in strong updrafts had balloon ascent rates of at least 15 m s 1 for at least 1 km these soundings had simpler electrical structures of 3 5 charge regions below 10 km altitude their maximum measured electric fields ranged from 85 to 130 kv m 1 the data may support an earlier hypothesis that charge is elevated in strong updrafts in addition the data may suggest that simpler charge structures are associated with proximity to strong updrafts rather than with different storm types

electrical and polarimetric radar observations of a multicell storm in telex abstract on 28 29 june 2004 a multicellular thunderstorm west of oklahoma city oklahoma was probed as part of the thunderstorm electrification and lightning experiment field program this study makes use of radar observations from the norman oklahoma polarimetric weather surveillance radar 1988 doppler three dimensional lightning mapping data from the oklahoma lightning mapping array lma and balloon borne vector electric field meter efm measurements the storm had a low flash rate 30 flashes in 40 min four charge regions were inferred from a combination of lma and efm data lower positive charge near 4 km and midlevel negative charge from 4 5 to 6 km msl from 0 to 6 5 c were generated in and adjacent to a vigorous updraft pulse further midlevel negative charge from 4 5 to 6 km msl and upper positive charge from 6 to 8 km from 6 5 to 19 c were generated later in quantity sufficient to initiate lightning as the updraft decayed a negative screening layer was present near the storm top

mesoscale convective systems 1 mesoscale convective systems mcss have regions of both convective and stratiform precipitation and they develop mesoscale circulations as they mature the upward motion takes the form of a deep layer ascent drawn into the mcs in response to the latent heating and cooling in the convective region the ascending layer overturns as it rises but overall retains a coherent layer structure a middle level layer of inflow enters the stratiform region of the mcs from a direction determined by the large scale flow and descends in response to diabatic cooling at middle to low levels a middle level mesoscale convective vortex mcv develops in the stratiform region prolongs the mcs and may contribute to tropical cyclone development the propagation of an mcs may have a discrete component but may further be influenced by waves and disturbances generated both in response to the mcs and external to the mcs waves of a larger scale may affect the propagation velocity by phase locking with the mcs in a cooperative mode the horizontal scale of an mcs may be limited either by a balance between the formation rate of convective precipitation and dissipation of stratiform precipitation or by the rossby radius of the mcv the vertical redistribution of momentum by an mcs depends on the size of the stratiform region while the net vertical profile of heating of the large scale environment depends on the amount of stratiform rain regional variability of the stratiform rain from mcss affects the large scale circulation s response to mcs heating

cloud to ground lightning in a tornadic storm on 8 may 1986 abstract on 8 may 1986 the national severe storms laboratory nssl collected doppler radar and lightning ground strike data on a supercell storm that produced three tornadoes including an f3 tornado in edmond oklahoma approximately 40 km north of nssl the edmond storm formed 30 km ahead of a storm complex and produced its first and most damaging tornado just as the storm complex began to overtake it from the west in the mesocyclone that spawned the tornado low level cyclonic shear peaked as the first tornado dissipated and a second tornado began as low level cyclonic shear initially increased negative cloud to ground lightning flash rates also increased reaching a peak of 11 min 1 a few minutes after the peak in cyclonic shear during this period lightning strike locations tended to concentrate just north of the mesocyclone near and inside a 50 dbz reflectivity core as cyclonic shear decreased from its peak during and after the second tornado negative ground flash rates also decreased and s

the june 22 tropical squall line observed during copt 81 experiment electrical signature associated with dynamical structure and precipitation the tropical convection experiment copt 81 convection profonde tropicale was carried out near korhogo northern ivory coast during may and june 1981 the june 22 squall line was observed using meteorological and electrical equipment the frontal part was characterized by a heavy precipitation core associated with strong convection it was followed by a region of weak precipitation and a wide area of stratiform rain the characteristic of this squall line resides in the two dimensional structure of the observed three dimensional wind fields with intense convection ahead of the heavy precipitation core electrical measurements indicate that electrostatic field changes at ground level occurred in the weak precipitation zone and in the stratiform precipitation region no particular electrical activity was observed in the most convective but shallow part of the squall line a classical dipole structure appeared within the stratiform area the stationary electrical structure was coherent with the stationary dynamics and precipitation pattern of the squall line

the ordovician igneous rocks with high sr y at the tongshan porphyry copper deposit satellite of the duobaoshan deposit and their metallogenic role abstract a strong link between high sr y arc magmas and porphyry cu mo au deposits has been recognized in recent years the tongshan and duobaoshan deposits are representative large cu mo au deposits in ne china we report la icp ms zircon u pb crystallization age of 471 5 1 3 ma for tongshan ore related granitoid re os isotopic analyses of the two chalcopyrite samples from tongshan deposit show a model age range of 470 2 477 1 ma the duobaoshan and tongshan ore related granitoids show higher sr y and la yb ratios the 34 s values of sulphides from the duobaoshan and tongshan deposits vary from 2 3 to 0 0 belonging to a magmatic hydrothermal system the pb isotopic ratios of the sulphides from the duobaoshan and tongshan deposit range from 17 201 to 18 453 for 206 pb 204 pb 15 445 to 15 551 for 207 pb 204 pb and 36 974 to 37 999 for 208 pb 204 pb indicating the addition of lower crustal material the duobaoshan and tongshan granitoids were formed in a subduction related continental arc setting produced by partial melting of juvenile hydrous basalts underplating the deep continental crust during the ordovician

caractere epigenetique etranger des gites filoniens pb zn ba f du district du bord sud du synclinorium de dinant belgique de nombreux indices et anciennes exploitations de faible tonnage pour pb zn ba f s observent dans les series carbonatees du devonien moyen et superieur du sw du synclinorium de dinant ou elles delimitent un district metallifere une etude lithogeochimique regionale des calcaires givetiens montre le faible potentiel metallifere de ces sediments de plateforme ces resultats sont confirmes par l etude de la distribution de 13 elements presents dans un filon et son encaissant immediat enfin la comparaison des compositions isotopiques du pb des galenes du filon et du pb en trace dans les calcaires encaissants apporte des arguments decisifs ces resultats sont suffisants pour rejeter l hypothese de l origine des metaux par secretion laterale et militent en faveur du caractere epigenetique etranger de ces mineralisations

deep mantle plume osmium isotope signature from west greenland tertiary picrites picrites from nuussuaq peninsula and qeqertarssuaq disko island west greenland preserve trace element and isotopic signatures reflecting the composition of the icelandic plume head os isotope ratios are low 187os 188os i 0 1272 0 1371 in terms of global plume related magmatism and this is coupled with anomalously high os abundances and radiogenic 143nd 144nd i isotopes crustally contaminated basalts within the west greenland sequences possess os and nd isotopic signatures consistent with mixing between initial plume head compositions and two discrete types of west greenland continental crust one crustal component is of a local sedimentary origin and the other is typical of ancient felsic crust the low os isotopic signatures of the picritic units are considered to be those of the initial mantle plume the fact that such low os isotope ratios occur in sequences with high 3he 4he and the non systematic variation in os isotopes with indices of fractionation accumulation and pb isotopes argue against mixing with depleted morb mantle or ancient subcontinental lithospheric mantle the high os concentrations in the picrites are attributed to high degrees of partial melting 25 of mantle containing no residual sulphide this is consistent with models for plume heads in which anomalous mantle temperatures initiate melting at high pressures generating large degrees of partial melting unradiogenic os and radiogenic nd components in plume related cfb magmatism may preserve contributions from a reservoir which is sampled only occasionally in young oceanic basalts such a reservoir shares os isotopic features with the primitive upper mantle pum which may also be manifest in the kea component of hawaiian magmatism therefore portions of the west greenland continental flood basalt province arguably represent the first direct sampling of unmodified plume head material derived from the lower mantle or lower portions of the upper mantle

electrification of stratiform regions in mesoscale convective systems part ii two dimensional numerical model simulations of a symmetric mcs abstract model simulations of a symmetric mesoscale convective system mcs observations discussed in part i were conducted using a 2d time dependent numerical model with bulk microphysics a number of charging mechanisms were considered based on various laboratory studies the simulations suggest that noninductive ice ice charge transfer in the low liquid water content regime characteristic of mcs stratiform regions is sufficient to account for observed charge density magnitudes and as much as 70 of the total charge in the stratiform region the remaining 30 is contributed by charge advection from the convective region the strong role of in situ charging is consistent with previous water budget studies which indicate that roughly 70 of the stratiform precipitation results from condensation in the mesoscale updraft thus both in situ charging and charge advection the two previously identified hypotheses appear to be important contributors to the electrical budget of the stratiform region the

experimental constraints on the partitioning of rhenium and some platinum group elements between olivine and silicate melt abstract we have performed partitioning experiments to assess the role of olivine in controlling the behavior of rhenium and the platinum group elements pges during basalt petrogenesis olivines were crystallized from an iron bearing basalt at 1 bar 105 pa and log fo2 of 2 6 4 9 and 7 4 fmq 4 3 2 and 0 5 respectively in situ analyses of olivine and glass by laser ablation inductively coupled plasma mass spectrometry la icp ms reveal a homogeneous distribution of ru rh pd re and pt but significant os heterogeneity at the m scale this latter behavior arises from the presence of undissolved os micronuggets suspended in the melt and included in olivine crystals olivine melt partition coefficients ds for re and the pges follow the order drh dru dpd dre dpt with decreasing fo2 rh and ru become more compatible with maximum partition coefficients of 2 6 and 2 respectively at log fo2 of 4 9 in contrast d values for pd become smaller with decreasing fo2 to a value of 0 006 at log fo2 of 7 4 olivine melt partitioning of rh ru pd re and pt derived from our experiments is confirmed by the behavior of these elements in lavas that have evolved by olivine fractionation an elastic strain model predicts the olivine melt partitioning of these elements excepting our measured value of dpt which is much lower the fo2 dependence on partitioning implies that at higher fo2 some portion of pges exist in higher valence states than predicted from their solubility

characteristics of lightning flashes associated with the charge layer near the 0 c isotherm in the stratiform region of mesoscale onvective systems

the behavior of gold in unaltered island arc tholeiitic rocks from izu oshima fuji and osoreyama volcanic areas japan high au concentrations 4 25 ppb in titanomagnetite concentrates from basalts and basaltic andesites of the izu oshima and fuji volcanic areas in the east japan arc indicate that au is strongly partitioned into titanomagnetite relative to the bulk rock the concentration of an in volcanic rocks increases during the early stages of fractional crystallization dominated by olivine pyroxenes and plagioclase but decreases with subsequent fractional crystallization involving titanomagnetite a delay in titanomagnetite formation during fractional crystallization subsequently results in comparatively high concentrations of au in island arc tholeftes wide variations in the au concentration are observed in rocks derived from primary magmas across a single volcanic area and these can be positively correlated with the concentrations of incompatible elements such as rb and zr these features are inherited from a s depleted mantle source since variable degrees of partial melting do not significantly affect the au concentrations of the primary magmas

thermodynamic properties of mesoscale convective systems observed during bamex dropsonde observations from the bow echo and mesoscale convective vortex experiment bamex are used to document the spatiotemporal variability of temperature moisture and wind within mesoscale convective systems mcss onion type sounding structures are found throughout the stratiform region of mcss but the temperature and moisture variability is large composite soundings were constructed and statistics of thermodynamic variability were generated within each subregion of the mcs the calculated air vertical velocity helped identify subsaturated downdrafts it was found that lapse rates within the cold pool varied markedly throughout the mcs layered wet bulb potential temperature profiles seem to indicate that air within the lowest several kilometers comes from a variety of source regions it was also found that lapse rate transitions across the 0 c level were more common than isothermal melting layers the authors discuss the implications these findings have and how they can be used to validate future high resolution numerical simulations of mcss

comparative geochemistry of rhenium in oxidized arc magmas and morb and rhenium partitioning during magmatic differentiation abstract the geochemical behavior of re in oxidized arc magmas eastern manus basin and morb has been reexamined in the early differentiation stage of oxidized arc magmas yb cu au ag and re have a bulk partition coefficient d between the crystallized mineral assemblage olivine clinopyroxene and plagioclase and the residual melt on the order of 0 33 d yb d au d re d ag d cu while in the late stage they have a bulk d between the crystallized mineral assemblage clinopyroxene plagioclase magnetite and monosulfide solid solution mss and the residual melt on the order d re d cu d au 1 d yb 0 29 d ag in oxidized arc magmas cu au and ag are primarily controlled by crystalline mss whereas re is primarily controlled by magnetite and it has a mss silicate melt partition coefficient significantly lower than 20 unlike oxidized arc magmas most morb are saturated with sulfide liquid based on the positive correlation of log d cu d re and fmq regardless of f s 2 log d cu d re 0 997 fmq 0 181 r 2 0 99 d partition coefficient between sulfide liquid and silicate melt fmq fayalite magnetite quartz oxygen buffer the partition coefficient of re between sulfide liquid and silicate melt for morb is estimated to be in the range of 600 10 000 at f o 2 of fmq to fmq 1 increasing with decreasing f o 2 these partitioning data constrain that during morb differentiation re may be as compatible as cu or ag at relatively oxidized conditions fmq 0 5 f o 2 f o 2

spatial and temporal evolution of horizontally extensive lightning discharges associated with sprite producing positive cloud to ground flashes in northeastern spain 1 during the evening of 6 august 2008 a small mesoscale convective system mcs entered the area of radar and 2 d interferometric lightning detection system coverage in northeastern spain and produced 17 sprites recorded by a camera at only 95 180 km distance this study presents an analysis of the in cloud component of the sprite associated lightning flashes and those of other flashes the analysis focuses on the horizontal development of sprite producing lightning by discussing three examples divided into the periods before the positive cloud to ground flash cg between cg and the end of the sprite and the period after the sprite location and horizontal size of sprites appear to be well explained by the temporal and spatial development of the lightning path the majority of sprite producing discharges started directly at the rear side of developing and mature convective cores within the decaying mcs either with the cg or with preceding negative leaders the cg started a burst of vhf sources during which the sprite developed delayed carrot sprites developed after a secondary smaller burst and were well collocated with the burst toward the rear of the mcs the order of development of elements in a grouped sprite followed the direction of lightning propagation during the burst stage the second part of the analysis concentrates on the metrics of sequences of vhf sources and shows that sprites are indeed produced by the largest longest lasting discharges with particularly large line perpendicular dimensions 37 km median compared with 11 km for cg 25 ka

lightning location relative to storm structure in a leading line trailing stratiform mesoscale convective system 1 horizontal and line normal vertical cross sections and composite images of dallas fort worth lightning detection and ranging ldar ii vhf radiation sources and radar reflectivity over a 30 min period provide a unique perspective on lightning pathways within a leading line trailing stratiform llts mesoscale convective system mcs on 16 june 2002 the overwhelming majority of vhf lightning sources occurred within the leading convective line in a bimodal pattern in the vertical assuming that vhf source density maxima were most likely associated with positive charge then the ldar ii observations suggest that the gross charge structure of the convective region of the mcs was characterized by a tripole with net positive charge centered at 4 5 km agl 3 c and 9 5 km agl 35 c and net negative charge centered roughly in the relative minimum of the vhf source density maximum at 7 km agl 17 c a persistent lightning pathway and inferred positive charge zone sloped rearward by 40 50 km and downward by 4 5 km from the upper vhf source maximum in the convective line through the transition zone and into the radar bright band of the stratiform region in the stratiform region vhf lightning sources and inferred positive charge were concentrated in three layers centered at 4 5 6 and 9 km agl 2 c 11 c and 31 c respectively consistent with past electric field studies of symmetric llts mcss positive cloud to ground lightning flashes in the stratiform region were initiated in the convective line and followed the slanting pathway from the top of convective cores to the stratiform precipitation where they were horizontally extensive layered and highly branched the sloping lightning pathway was identical to hypothetical trajectories taken by snow particles these observations provide further support for the advection of charge on snow along the sloping pathway and the in situ generation of charge in the horizontal lightning layers as primary contributors to electrification and positive lightning production rearward of the convective line

cloud to ground lightning activity in the 10 11 june 1985 mesoscale convective system observed during the oklahoma kansas pre storm project abstract as part of the field program for the oklahoma kansas pre storm project conducted in may june 1985 a network of electromagnetic direction finders was deployed to locate and detect the polarity of cloud to ground cg lighting flashes associated with mesoscale convective systems mcss we present an analysis of such data for the 10 11 june mcs this storm consisted of a line of convective cells trailed by an 80 km wide stratiform precipitation region data from the lightning strike locating network along with both conventional and doppler radar data are analyzed over a significant portion of the storm s lifetime to examine the relationship between the storm precipitation structure and the position and polarity of the lighting activity the majority of the negative cg activity is located in the convective precipitation region the frequency of negative cg activity is highest around the period of most intense convective rainfall positive cg activity is mainly confined to the trailing stratiform

electrical and kinematic structure of the stratiform precipitation region trailing an oklahoma squall line abstract an electric field sounding through the transition zone precipitation minimum that trailed an oklahoma squall line on 18 june 1987 provides information about the electrical structure within a midlatitude trailing stratiform cloud a single doppler radar analysis concurrent with the flight depicts a kinematic structure dominated by two mesoscale flow regimes previously identified in squall line systems a strong midlevel front to rear flow coinciding with the stratiform cloud layer and a descending rear inflow that sloped from 6 5 km agl at the stratiform cloud s trailing edge to 1 5 km agl at the convective line electric field magnitudes as high as 113 kv m 1 were observed by the electric field sounding which reveals an electric field structure comparable in magnitude and complexity to structures reported for convective cells of thunderstorms the charge regions inferred with an approximation to gauss law have charge density magnitudes of 0 2 4 1 nc m 3 and vertical thicknesses of 130 1160 m