poleward displaced electron precipitation from lightning generated oblique whistlers new simulation results show that obliquely propagating lightning generated whistlers which fill vast volumes of the magnetosphere readily induce significant energetic electron precipitation over large regions of the ionosphere depositing appreciable energy flux to the upper atmosphere at locations substantially poleward of the lightning source these results provide a new interpretation for the observed spatial relationships between lightning discharges and subsequently disturbed ionospheric regions inferred from subionospheric signal perturbations i e trimpi events reported in several lightning induced electron precipitation lep studies

earthquake faulting as a structural process abstract structural geology is concerned with the history of movement in the earth s crust and the processes by which displacements occur in the upper one third to one half of deforming continental crust displacement is accommodated largely by seismic slip increments on existing faults it follows that earthquakes and related processes are an integral part of structural geology traditionally structural geologists have been preoccupied with the complexity of the finite deformation within fault zones and with the stress states prevailing at the initiation of faults in intact crust future structural work should be directed more towards understanding the dynamic character of fault reactivation during incremental slip and related effects questions of interest include rheological and geometrical controls on the initiation perturbation and termination of ruptures directivity effects associated with rupture propagation the recognition of structures resulting from repeated stress cycling within seismogenic crust and identification of structural features diagnostic of shear stress levels during faulting structures arising from the inter relationships between slip episodes and induced fluid flow are of special importance because these dynamic fault processes appear influential in the development of much fault hosted mineralization mesothermal gold quartz lodes hosted in high angle reverse shear zones of mixed brittle ductile character form illustrative examples of structures that arguably can only be interpreted by seismo structural analysis embodying the concepts listed above

geochemistry of precambrian carbonates i archean hydrothermal systems abstract carbonate rocks from the superior and slave provinces of canada kaapvaal craton of south africa and the pilbara block of australia considered of hydrothermal origin from field criteria have been characterized mineralogically isotopically sr o c and chemically major and trace elements in agreement with previous studies the bulk chemical composition suggests that the carbonate rocks originated by massive carbonatization silicification and k na metasomatism of intermediate to ultramafic silicate precursors the carbonate component itself defines two partially overlapping populations the ferroan dolomite breunnerite assemblage is confined mostly to shear zones conduits and stockworks while the calcite ferroan dolomite ankerite siderite mineral assemblage represents a wider regional halo this dichotomy may result from a multistory not necessarily coeval plumbing system of the volcanosedimentary piles with the regional halo population being a product of shallow circulation cells while the conduit assemblage probably formed from deeper focussed flows trace element chemistry of carbonates is consistent with their precipitation from relatively low salinity solutions 2 sea water and with derivation of solutes from the contemporaneous volcanosedimentary piles 87 sr 86 sr 0 7020 0 0008 the hydrothermal waters were derived either from metamorphic dewatering at the base of the piles or from a magmatic source with 18o of about 6 7 smow in contrast carbon dioxide in the regional and the conduit assemblages had dissimilar principal sources in the former it was derived from exogenic sources decarbonation of marine carbonates and thermal decomposition and oxidation of organic matter while in the latter the co2 was of mantle origin 13c of 2 to 10 and 4 2 pdb respectively

radiation belt electron precipitation fluxes associated with lightning in this study we consider the dependence of precipitation fluxes arising from whistler induced radiation belt losses on the strength of the associated lightning s return stroke current as a result of this work it will be possible to use lightning activity data sets to estimate globally induced precipitation flux rates and thus determine the lightning induced effect on the radiation belts more accurately four study days were selected during which a high proportion of the lightning activity occurring near the east coast of north america produced observable trimpi effects on vlf transmitter signals propagating in the region of the antarctic peninsula similar tol 2 2 5 the lack of lightning in antarctica gives this location a unique advantage for this study the functional dependence of the relative scattered field amplitude with the return stroke peak current of the lightning discharge suggests that during these events diffusion conditions are occurring near the precipitating radiation belt particles loss cone due to strong whistler wave fields probably caused by ducted signals the range of observed trimpi scatter amplitude of 10 to 35 db was produced by precipitation bursts with energy fluxes estimated to range over 6 5 0 4 x 10 3 ergs cm 2 s 1 the largest fluxes were found to be driven by lightning currents of about 250 ka while the smallest detectable fluxes relate to lightning currents of 70 ka although 3 of the 4 study days showed a high degree of consistency between the levels of lightning return stroke peak current required to produce any given perturbation scatter amplitude value conditions were significantly different on 23 april 1994 on this day observed trimpi signatures were 6 7 db greater for any given lightning intensity than on the other study days these events are consistent with a significantly harder radiation belt precipitation spectra probably caused by geomagnetic storm time acceleration processes of radiation belt electrons

pore water evolution during sediment burial from isotopic and mineral chemistry of calcite dolomite and siderite concretions abstract coal measures often contain concretions segregations of diagenetic minerals originally formed within unconsolidated sediments three different types calcite pyrite dolomite pyrite and siderite occurring spatially quite close together in the central pennine region of england vary widely in carbon isotope composition 10 35 13c 21 49 and in major cation chemistry ca mg fe mn within some siderite concretions very high mn fe ratios were found in central subsamples these were also most enriched in 13c the fe mg ratio decreases systematically from centre to edge early shallow to deeper later precipitation the calcite pyrite and dolomite pyrite concretions developed completely prior to significant burial both have high mn fe ratios but negative 13c values calcite 21 49 dolomite 8 67 to 10 48 all of these patterns can be equated precisely with theories of pore water evolution developed on the basis of geochemical investigations of modem sediments microbial processes sulphate reduction methanogenesis contributed significantly as did thermal decarboxylation to siderite precipitated at considerable burial depth mn iv and fe iii acted differentially as oxidants producing co2 and increasing alkalinity the interplay of fresh and marine depositional waters is seen most obviously in the presence or absence of sulphate reduction this controlled mineral type iron sulphide or carbonate as well as isotopic and mineral chemistry

a stable isotope study of magnesites from the rum jungle uranium field australia implications for the origin of strata bound massive magnesites the contrast between the scanty magnesite deposition in modern sedimentary environments and the large strata bound magnesites of the past constitutes a magnesite problem which unlike the dolomite problem has so far attracted little attention from the geologists magnesite beds up to 700 m thick from the lower proterozoic rocks of the rum jungle uranium field northern territory of australia offer attractive circumstances for studying the isotope systematics of coarse crystalline magnesite and coexisting dolomite magnesites yield 18o and 13c compositions of 11 2 to 14 6 smow and 1 0 to 5 8 pdb respectively dolomites yield 18o and 13c values of 11 7 to 21 9 and 4 0 to 2 9 respectively and show an 18o enrichment gradient away from the magnesite fluid inclusion homogenization temperatures used in conjunction with the isotope determinations and an approximate magnesite water equation indicate that magnesites were formed in the temperature range of 100 200 c from fluids that became progressively enriched in 18o the results support an epigenetic metasomatic replacement model of dolomite by magnesite under the influence of invasive hot mg rich basinal fluids strata bound massive magnesites which abound particularly in archean proterozoic rock sequences generally preserve the sedimentary structures but do not retain primary isotopic compositions and are therefore unsatisfactory indicators of oceanic isotope evolution and ocean paleotemperatures

nomenclature for iron formations abstract this paper explains the terminology and a classification scheme which are used in an accompanying paper about the genesis of iron formations an iron formation is considered to be a stratigraphic unit which consists mostly of iron rich chemical sedimentary rock specifically rock with more than 15 fe the rock is called ironstone iron formations may be classified into six groups on the basis of the sedimentary environment in which they accumulated some previous authors have used the terms ironstone and iron formation in more restricted ways for example ironstone has been used to name one of the six environmental types of iron formations and iron formation has been used exclusively for chert rich iron formations these restrictions are avoided herein because they are not consistent with the simplicity of the names by analogy with limestone ironstone is simply an iron rich chemical sedimentary rock the word formation clearly refers to a stratigraphic unit and so iron formation is applied to any stratigraphic unit which is composed predominantly of ironstone alternative usages of the terms ironstone and iron formation have been sufficiently varied that none of the usages can be defended on the grounds of overwhelming support independent of semantic arguments

occurrence and significance of magnesite in upper permian guadalupian tansill and yates formations delaware basin new mexico magnesite mgco 3 occurs pervasively in a 270 ft 82 m cored interval of upper permian guadalupian shelf deposits from the northern rim of the delaware basin portion of the permian basin new mexico in our core example magnesite is found in tidal flat lagoon and pisolite shoal dolomites and siltstones of the tansill and uppermost yates formations the interval is overlain by magnesite bearing anhydrite and a thick halite section of the ochoan salado formation the basinwide extent of magnesite is unknown the texture of magnesite in core slabs thin sections and sem scanning electron microscope mounts is nearly identical to that of dolomite the magnesite consists of anhedral to euhedral crystals ranging in size from 1 to 4 mm within the dolomite intervals of the core magnesite occurs in three forms 1 patches of crystals and as replacement of allochems both in an otherwise dolomite matrix 2 pervasive replacement of host dolomudstone and peloidal and pisolitic dolowackestone packstone and 3 discrete layers interbedded with anhydrite magnesite rarely fills pore spaces in dolomite but within siliciclastic beds magnesite occurs both as a first generation cement and as a replacement of carbonate grains magnesite and dolomite are mutually exclusive in siliciclastic beds wi hin the core and magnesite occurs only where anhydrite is abundant magnesite may have formed either 1 during ochoan deposition or thereafter after burial of the tansill and yates formations from dense brines originating from the overlying salado evaporites or less likely 2 syndepositionally with the tansill and yates sediments preliminary measurements of stable carbon and oxygen isotopes for magnesite yield normal permian values for sigma 13 c averaging 6 84 parts per mil pdb and slightly evaporitic values for sigma 18 o averaging 1 04 parts per mil pdb corrected 87 sr 86 sr isotope composition averages 0 70687 because a high content of associated uranium in the magnesite rich part of the core causes large gamma ray deflections similar to those for shale and because the density of magnesite is close to that of anhydrite the presence of magnesite could lead to improper evaluation of lithology and porosity from logs and could ultimately result in failure to recognize potential reservoir zones

remote sensing of ionospheric disturbances associated with energetic particle precipitation using the south pole vlf beacon 1 the stanford university vlf beacon transmitter located at south pole operates at 19 4 khz transmitting for 1 min intervals every 15 min throughout the day the beacon serves as a tool to measure changes in the d region ionospheric conductivity owing to energetic particle precipitation and is capable of providing coverage that spans the antarctic continent we present vlf beacon signal amplitude and phase data measured at palmer station antarctica diurnal and seasonal variations are discussed first followed by analysis of data from two periods of high geomagnetic activity in july 2004 and in may 2005 with a phase advance and an amplitude depression of the beacon signal as recorded at palmer observed for both cases data from the meped instrument aboard the noaa 16 and 17 poes satellites show an increase in energetic electron 100 kev and proton 16 mev precipitation fluxes coincident with the vlf beacon signal perturbations the fluxes measured on poes are used as an aide to generate profiles of secondary ionization along the great circle path from south pole to palmer these profiles are then applied to a quantitative model of subionospheric vlf signal propagation to estimate the phase and amplitude variations expected results indicate that the observed vlf amplitude and phase data are in reasonable agreement with theoretical calculations in both cases indicating that the model captures the ionospheric disturbance in effect during both of the disturbed periods

the sulfur and carbon isotope composition of scapolite rich granulites from southern tanzania sulfur and carbon isotope data are presented of 15 granulite samples from the furua complex southern tanzania in which scapolite is a primary and major rock forming constituent up to 30 vol from these data the isotopic composition is deduced of the sulfate and carbonate group in the scapolite structure subsequently the composition and origin is discussed of the volatile species that are present in the deep crustal environment in which these scapolites formed

archean gold relation to granulite formation or felsic intrusions two current models for archean au deposits appeal to granulitization or magmatic processes but new data reveal that neither of these schemes is viable most tonalitic archean granulites are characterized by primary large ion lithophile element lile depletion and so there is no complementary relation to lile enrichment in au deposits nor are k rb k ba k li k cs and th u systematics of granulites and gold deposits complementary published c isotope systematics and c he flux calculations do not support the model of granulitization by influx of mantle c0 2 nor is the total population of 13 c values of au deposits comparable to mantle co 2 or the granulite c reservoir archean tonalite trondhjemite granodiorite ttg magmas are characterized by uniform 87 sr 86 sr whereas the deposits range between 0 701 and 0 720 and average 13 c ranges between 9 and 0 4 with provinciality of sr o and c isotopic signatures moreover fractionated granites trend to normal k rb but higher rb sr and k ba ratios whereas the gold deposits are characterized by main trend or higher k rb and k ba ratios coupled with little cs li or tl enrichment and scattered rb sr ratios many of the deposits postdate the stocks with which they are associated by 20 to 30 m y the variable sr pb c and o isotope systematics but uniform lile trends reflect equilibration of internally or externally derived fluids with compositionally variable crust at low water rock ratios in transpressive accretionary regimes

assessing climate change impacts on the stability of small tidal inlets part 2 data rich environments climate change cc is likely to affect the thousands of bar built or barrier estuaries here referred to as small tidal inlets stis around the world any such cc impacts on the stability of stis which governs the dynamics of stis as well as that of the inlet adjacent coastline can result in significant socio economic consequences due to the heavy human utilisation of these systems and their surrounds this article demonstrates the application of a process based snap shot modelling approach using the coastal morphodynamic model delft3d to 3 case study sites representing the 3 main sti types permanently open locationally stable inlets type 1 permanently open alongshore migrating inlets type 2 and seasonally intermittently open locationally stable inlets type 3 the 3 case study sites negombo lagoon type 1 kalutara lagoon type 2 and maha oya river type 3 are all located along the southwest coast of sri lanka after successful hydrodynamic and morphodynamic model validation at the 3 case study sites cc impact assessment are undertaken for a high end greenhouse gas emission scenario future cc modified wave and riverflow conditions are derived from a regional scale application of spectral wave models wavewatch iii and swan and catchment scale applications of a hydrologic model clsm respectively both of which are forced with ipcc global climate model output dynamically downscaled to 50 km resolution over the study area with the stretched grid conformal cubic atmospheric model ccam results show that while all 3 case study stis will experience significant cc driven variations in their level of stability none of them will change type by the year 2100 specifically the level of stability of the type 1 inlet will decrease from good to fair to poor by 2100 while the level of locational stability of the type 2 inlet will also decrease with a doubling of the annual migration distance conversely the stability of the type 3 inlet will increase with the time till inlet closure increasing by 75 the main contributor to the overall cc effect on the stability of all 3 stis is cc driven variations in wave conditions and resulting changes in longshore sediment transport not sea level rise as commonly believed

scattering pattern of lightning induced ionospheric disturbances associated with early fast vlf events simultaneous observations of early fast very low frequency vlf events at nine closely spaced 65 km sites are used together with a numerical model of the propagation and scattering of vlf signals in the earth ionosphere waveguide to directly measure the scattering pat tern of associated ionospheric disturbances in cases when the causative lightning is within 700 km of the north south array of observing sites early fast vlf events are typically observed at no more than 2 or 3 sites which indicates a nar row beam of the scattered signal in the forward direction in the dierent cases studied forward scattering patterns exhibit 15 db beamwidths of less than 30 consistent with horizontal extent of 90 30 km

origin of ultramafic hosted vein magnesite deposits abstract large deposits of magnesite mgco3 occur either as carbonated ultramafic rocks or as sedimentary beds the origins of both sedimentary and ultramafic hosted deposits remain controversial as does the relationship between them ultramafic hosted deposits are reviewed herein with an emphasis on veins rather than massive bodies magnesium apparently has been supplied to magnesite veins by their ultramafic host uncertainties concerning ultramafic hosted deposits include the source state and mode of transportation of carbon the cause of its precipitation and the mineralogy of the initial precipitate genetic questions about ultramafic hosted vein deposits are summarized with the aid of flow charts the preferred route through these charts attributes most vein magnesite to an influx of metamorphic degassing co2 and ch4 into groundwater which flows through serpentinite or peridotite the source of co2 ch4 is considered to be deeper than 10 km because metamorphism 300 c is required to release carbonaceous volatiles of the type which apparently induced observed magnesite mineralization however vein magnesite precipitation generally has occurred within just a few hundred meters of the earth s surface vein deposits are considered to be genetically related to massive bodies but the massive bodies typically contain less 12c the 12c rich co2 which has produced vein deposits is attributed to a fluid phase variably mixed ch4 co co2 which rose until it reached upper crustal groundwater the hypothetical water poor fluid presumably became slightly oxidized hence richer in soluble co2 as it encountered near surface sulfate bearing water co2 enriched water is envisioned to have been expelled regionally due to tectonic processes leaving little mineralogical evidence of its expulsion through non ultramafic rock co2 rich water which happened to encounter either serpentinite or peridotite presumably has produced magnesite vein deposits and a common silicate byproduct nontronite according to the following reaction 12 mg3si2o5 oh 4 serpentine 36 hco3 4 fe3o4 o2 12 fesi2o5 oh nontronite 36 mgco3 magnesite 36 oh 18h2o

on the relationship between lightning peak current and early vlf perturbations 1 lightning strokes are known to cause direct heating and ionization of the d region some of which are detected via scattering of vlf transmitter signals and are known as early vlf events the disturbed ionosphere typically recovers in many tens of seconds new experimental evidence is presented demonstrating that the scattering pattern and onset amplitude of early vlf events are strongly related to both the magnitude and polarity of causative lightning peak current observations of early vlf events at nine stanford vlf receiver sites across the continental united states are combined with lightning geolocation data from the national lightning detection network nldn during january and march 2011 nldn recorded 7769 intense lightning discharges with high peak currents 100 ka generating 1250 detected early vlf events we show that the size of the scattered field due to the ionospheric disturbance increases with the peak current intensity of the causative lightning discharge the most intense peak currents of 200 and 250 ka disturb vlf transmitter signals as far as 400 km away from the lightning stroke early vlf event detection probability also increases rapidly with peak current intensity on the other hand the observed vlf amplitude change is not significantly dependent on the peak current intensity stroke polarity is also important with positive strokes being 5 times more likely to generate early vlf disturbances than negative strokes of the same intensity intense positive cloud to ground lightning discharges especially when occurring over the sea are also more likely to produce early vlf events with long recovery many minutes

cathodoluminescence of magnesite examples from the eastern alps although cathodoluminescence cl microscopy is routinely used in studies of carbonate diagenesis this technique is rarely applied to the petrographic study of magnesitic rocks encouraging results however were obtained from very low grade metamorphic magnesite samples from the eastern alps crystal growth textures unrecognizable in transmitted light became clearly visible when a hot cathode device was used spectrophotometric measurements show that mn 2 is the only activator producing a broad emission peak at about 652 nm microprobe analyses indicate that the different cl intensities are controlled mainly by variations in the concentrations of fe 2 because mn 2 concentrations are consistently high quenching of luminescence follows a logarithmic function and magnesite containing more than 6 5 wt feo corresponding to 7 5 mol feco 3 was found to be nonluminescent i e levels of cl were below detection

diagenetic trends in the siliceous facies of the monterey shale in the santa maria region california x ray diffraction and oxygen isotopic analyses of outcrop and subsurface samples of siliceous rocks were used to reconstruct thermal and diagenetic histories of the miocene monterey shale near santa maria california within many stratigraphic sections soft porous diatomaceous rocks change gradationally to underlying hard and brittle chert porcellanite and siliceous shale the accompanying silica mineral zones are in descending stratigraphic order 1 biogenic silica opal a 2 cristobalitic silica opal ct and 3 microcrystalline quartz boundaries between silica mineral zones and stratigraphic horizons are often discordant within the opal ct zone the d 101 spacing of opal ct decreases in a smooth non linear fashion from about 4 10 a to 4 04 a in the santa maria valley and bradley oil field areas the thicknesses of the opal ct zones are greater and the present thermal gradients less than in the adjacent orcutt oil field thin opal ct zones at shallow maximum burial depths apparently correlate with higher thermal gradients using present thermal gradients and reconstructed maximum burial depths from well data in the santa maria region the ranges in temperatures for the top and base of the opal ct zone are 38 54 c and 55 110 c respectively the temperature difference between these two boundaries ranges from 17 to 60 c in comparison temperature ranges for these two boundaries computed from oxygen isotopic compositions of opal ct and quartz extrapolated experimental quartz water fractionations and assuming o18 0 o for the isotopic composition of the equilibrating fluid are 18 56 c and 31 80 c for the top and base of the opal ct zone respectively the temperature difference between these boundaries is 11 36 c using this method thermal gradients and sedimentation rates strongly influence rates of silica transformations reconstructed thermal and diagenetic histories of siliceous rocks of the monterey shale at four well sites in the santa maria region demonstrate that most silica conversions probably occurred during the last 3 4 myr in response to accelerated rates of sedimentation and therefore burial heating during the pliocene

subionospheric vlf signatures of oblique nonducted whistler induced precipitation subionospheric very low frequency vlf signal perturbations observed at multiple sites in association with individual lightning discharges exhibit onset delays which steadily increase with increasing l value the timing of the onsets and the inferred spatial extent 1000 km of the ionospheric disturbance are consistent with those expected for electron precipitation induced by obliquely propagating i e nonducted whistlers

a stable isotope study of the hydrothermal alteration of the east taiwan ophiolite abstract the east taiwan ophiolite eto occurs as allochthonous fragments in the lichi melange and has been suggested to have formed at an active ridge ridge transform fault in a marginal basin the brecciated plutonic sequence has experienced a pre brecciation ocean ridge type high temperature metamorphism as well as a post brecciation off axis type low temperature metamorphism whereas the extrusive sequence has been subjected only to an off axis low temperature hydrothermal alteration stable isotopic studies of the eto show a slightly decreasing trend in oxygen isotope compositions from basalt through plagiogranite gabbro to ultramafic rocks the isotopic compositions of the eto basalts indicate low temperature interaction with seawater under variable water rock ratios the amphiboles from the eto gabbro show low 18o i e 3 1 to 3 8 and high d i e 19 to 9 values this is interpreted as having resulted from high temperature interaction with seawater derived hydrothermal fluid the plagioclase in the gabbro is mostly albitic in composition and exhibits very high 18o values i e 12 0 which may have resulted from low temperature reaction with 18o enriched fluid such 18o enriched fluid may have been derived from a high temperature seawater plutonic rock interaction system the antigorite and lizardite chrysotile serpentinites in the eto formed in oceanic environments under pre and post brecciation metamorphic conditions respectively the isotopic compositions of the antigorite are compatible with its formation in an oceanic environment although the 18o values of the lizardites chrysotiles are comparable to those of oceanic serpentines their d values ranging from 91 to 57 are too low to be accounted for by reaction with seawater derived fluid post formation hydrogen isotope exchange between the lizardite chrysotile and local meteoric waters during after on land emplacement of the serpentinites is postulated as a probable explanation calcite veins are ubiquitous in the eto three carbon sources are identified inorganic seawater carbon juvenile carbon and organic carbon in the last case it is shown that some calcite veins may contain a substantial amount of co2 derived from the ch4 oxidation process the organic carbon was most likely derived from organics in the surrounding lichi mudstone therefore the calcite veins with an organic carbon signature are suggested to have formed after the eto emplacement within the lichi melange

origin of nitrogen rich natural gases in the california great valley evidence from helium carbon and nitrogen isotope ratios abstract dry natural gases produced from the sacramento and northern san joaquin basins contain up to 87 nitrogen 15n measurements for gases with n2 8 vary from 0 9 to 3 5 methane 13c values vary from 61 to 15 3 he 4 he ratios indicate the presence of mantle derived helium in addition to radiogenic crustal helium and suggest that the gases may originate from mixing between three principal components a hydrocarbon rich gas with 3 he 4 he 0 1r a derived from the microbial and thermogenic alteration of sedimentary organic matter a hydrocarbonrich gas with 3 he 4 he 2 75r a derived from the localized pyrolysis of sediments by magmatic volatiles and a nitrogenrich gas with 3 he 4 he 1r a the nitrogen rich component is characterized by methane 13c less negative than 25 and n 2 ar ratios as high as 22 000 nitrogen concentrations tend to increase towards the basement along the shallow eastern margin of the valley suggesting that the nitrogen rich component is derived from metasedimentary rocks deep within the crust the coast ranges fraciscan complex which was thrust well beneath the great valley during late mesozoic and early cenozoic subduction appears to be the most likely source

spheroidal dolomites origin by hydrocarbon seepage spheroidal dolomite cements are a pervasive and distinctive feature in five exposed lithologies of different geological age in kuwait the spheroids range in diameter from 5 350 m have concentric zones and nuclei of fluid inclusions with or without a radial fabric and compositions varying from near stoichiometric to ca56 mg44 all spheroids appear to be primary in origin with no evidence of replacement some concentric zones show selective calcitization and or leaching most of these features are confined to within 30 m of the surface consequently spheroidal dolomites recognizable at depth in ancient sequences may be indicative of a local unconformity the dolomite distributions are areally correlative with known areas of hydrocarbon seepage the latter being confined to prominent oil field anticlinal trends it is proposed that the dolomitization was caused by groundwaters carrying hydrocarbons to the surface which were then oxidized to carbon dioxide the gas bubbles may have acted as nuclei for spheroid growth with a possible inducement by bacteria which have an affinity for hydrocarbons the implication is that the regional distribution of spheroidal dolomites may be an indicator of a potential reservoir facies at depth

deep fluid circulation in alpine shear zones pyrenees france field and oxygen isotope studies a combined field stable isotope and whole rock chemical study was made on late cretaceous to tertiary metasomatic shear zones cutting hercynian gneisses in the aston massif pyrenees france mylonitisation occurred during the early stages of alpine compression under retrograde conditions at 400 450 c and about 10 km depth whole rock 18o values of 11 to 12 in the gneisses was lowered to 5 to 9 in the shear zones with the quartz muscovite 18o 16o fractionations of about 2 to 4 essentially unchanged these 18o 16o systematics together with d muscovite 40 to 50 indicate that large volumes of formation waters or d rich meteoric waters passed through the shear zones during deformation the same fluids also redistributed major elements as shown by the correlation of 18o shift with muscovitisation and albitisation reactions in granitic wall rocks however even though 18o was universally lowered within the shear zones the 18o 16o ratios were not homogenised nor do they correlate in detail with the presence or absence of muscovitisation suggesting that fluid flow was probably fracture controlled and episodic field mapping shows that along the length of a particular shear zone muscovitisation of granite gneiss dies out 150m above the contact with underlying sillimanite gneiss thus muscovitisation and albitisation of granite gneiss in shear zones and their wall rocks probably occurred during re equilibration of acidic chloride rich aqueous fluids that had previously moved upward within the shear zones through underlying sillimanite gneiss extremely high material balance fluid rock ratios 103 are required to explain the extent of muscovitisation along this shear zone implying integrated fluid mass fluxes of about 108 kg m2 this is probably close to the maximum value for other shear zones in the network similar volumes of a more chemically evolved fluid must have passed through the unmuscovitised mylonites showing that the absence of alteration cannot necessarily be used to infer low values of fluid flux for reasonable pressure gradients and time scales of fluid movement effective permeabilities of 10 15 to 10 17 m2 are required such values can be accounted for by short lived widely spaced cracks produced during seismic activity a model is presented in which formation waters were seismically pumped down an underlying shallow southward dipping decollement and then upward through the steeply dipping shear zone network

correlation between global lightning and whistlers observed at tihany hungary although the generation and propagation mechanisms for whistlers are fairly well understood the location and extent of the lightning source region for the whistlers observed at a given station are

present day tectonics of the southeastern caribbean and northeastern venezuela four telemetered seismic arrays were operated in northeastern venezuela during the summer of 1979 an analysis of the data collected has resulted in accurate locations for about 100 microearthquakes and four new focal mechanism solutions on the basis of these new data an in depth analysis of teleseismic data and geologic evidence we propose a new plate tectonic framework for the southeastern caribbean in this model underthrusting of the atlantic seafloor along the lesser antilles is extended to the southeast of trinidad the subducted slab is shown to dip northwesterly beneath trinidad and the caribbean sea penetrating depths of at least 150 km this subduction appears to terminate abruptly in the vicinity of the los bajos el soldado fault zone which trends wnw nw and is located in the gulf of paria west of trinidad geologic evidence shows right lateral strike slip rlss motion in this fault zone probably initiated in the late pliocene this wnw nw trending fault zone joins up with the e w trending el pilar casanay fault system in northeastern venezuela which also moves right laterally the el pilar fault is apparently offset by nnw trending faults that exhibit rlss motion as well as normal faulting this complex motion on an en echelon series of faults is interpreted to be the result of wnw motion of south america relative to the caribbean plate in our interpretation the e w component of relative motion is accommodated by rlss motion on e w faults and results in normal faulting on nnw sse faults the smaller component of n s convergence is reflected by rlss motion on nnw trending faults and is accommodated by some internal deformation the timing of the initiation of rlss motion on the los bajos fault zone and the known total amount of displacement on it as well as other geologic indicators lead us to suggest that this complex mode of strike slip motion began only a few m y ago and that the average rate of relative plate motion in this region is probably 0 9 0 2 cm yr

electron precipitation events driven by lightning in hurricanes 1 in mid september of 2003 hurricane isabel passed through the great circle path gcp of a subionospherically propagating lf signal between the nau transmitter in puerto rico and a receiver located outside boston cloud to ground lightning flashes detected by the long range lightning detection network lrldn and located in the outer rainbands of the hurricane were associated with perturbations in the received lf signal consistent with lightning induced electron precipitation lep events the number of perturbations detected on the lf signal exhibiting the known characteristics rapid onset followed by slow recovery of lep events tended to increase with the occurrence of hurricane associated lightning near the gcp the majority 65 of causative lightning flashes those flashes recorded in the lrldn data that were time correlated with spherics associated with lep events in the vlf lf data occurred within 500 km of the gcp and those flashes associated with isabel typically occurred in the outer rainbands of the hurricane while lightning generally occurs more frequently in the outer rainbands of hurricanes than in other tropical oceanic storms there is no indication that the hurricane associated lightning is more likely to induce electron precipitation events than lightning associated with other storm systems hurricane floyd in september of 1999 and hurricane fabian in august september of 2003 also passed near the gcp of subionospherically propagating vlf lf signals and the received signals exhibited similar perturbation patterns